LIBRARY 

OF   THK 

UNIVERSITY  OF  CALIFORNIA. 

.  GIRT  OR 


...    U/TUyv-t^^ 
94199  Class 


gale  'Bicentennial  publications 
STUDIES 


FROM  THE 


CHEMICAL  LABORATORY   OF  THE  SHEFFIELD 
SCIENTIFIC    SCHOOL 


gale  'Bicentennial  publications 

With  the  approval  of  the  President  and  Fellows 
of  Yale  University,  a  series  of  volumes  has  been 
prepared  by  a  number  of  the  Professors  and  In- 
structors, to  be  issued  in  connection  with  the 
Bicentennial  Anniversary,  as  a  partial  indica- 
tion of  the  character  of  the  studies  in  which  the 
University  teachers  are  engaged. 

This  series    of  volumes    is    respectfully   dedicated  to 

0raDttatrs  of  tfjr  Unitirrsitp 


STUDIES 


FROM  THE 


CHEMICAL   LABORATORY 

OF  THE 

SHEFFIELD  SCIENTIFIC  SCHOOL 


EDITED  BY 

HORACE    L.    WELLS 

Professor  of  Analytical  Chemistry  and  Metallurgy 


VOLUME   I. 


OF  THE 

UNIVERSITY 

OF 

NEW  YORK:    CHARLES   SCRIBNER'S  SONS 

LONDON:   EDWARD   ARNOLD 

1901 


Copyright,  1901, 
BY  YALE    UNIVERSITY 

Published,  October,  iqoi 


UNIVERSITY  PRESS    -    JOHN    WILSON 
AND    SON    •     CAMBRIDGE,    U.S.A. 


PREFACE 

THE  object  of  this  publication  is  to  show  what  the  Sheffield 
Chemical  Laboratory  has  done  and  is  doing  in  the  way  of 
scientific  research,  and  to  bring  together  some  of  the  more  recent 
papers  in  several  lines  of  work  in  a  form  convenient  for  study 
and  reference.  A  bibliography  is  given  which  shows  the  work 
of  the  present  officials  during  their  connection  with  the  labora- 
tory, while  a  selection  of  articles  that  have  been  published 
during  the  past  ten  years,  or  are  soon  to  appear,  forms  the  main 
part  of  the  book.  A  brief  historical  sketch  of  the  laboratory 
is  also  presented. 

H.  L.  W. 


TABLE    OF    CONTENTS 

VOL.  I. 

PAGE 
SHEFFIELD  LABORATORY  .  1 


BIBLIOGRAPHY 4 

PAPERS  ON  GENERAL  INORGANIC   CHEMISTRY: 

ON  A  SERIES  OF  CAESIUM  TRIHALIDES.  By  H.  L.  Wells. 

INCLUDING  THEIR  CRYSTALLOGRAPHY.  By  S.  L.  Penfield  13 

ON  THE  RUBIDIUM  AND  POTASSIUM  TRIHALIDES.  By  H.  L. 
Wells  and  H.  L.  Wheeler.  WITH  THEIR  CRYSTALLOGRA- 
PHY. By  S.  L.  Penfield 33 

ON  THE  ALKALI-METAL  PEXTAHALIDES.  By  H.  L.  Wells  and 
H.  L.  Wheeler.  WITH  THEIR  CRYSTALLOGRAPHY.  By 
S.  L.  Penfield 48 

ON  SOME  ALKALINE  IODATES.  By  H.  L.  Wheeler.  WITH 

CRYSTALLOGRAPHIC  NOTES.  By  S.  L.  Penfield  ....  58 

ON  A  METHOD  FOR  THE  QUANTITATIVE  DETERMINATION 
OF  CAESIUM,  AND  THE  PREPARATION  OF  PURE  CAESIUM 
AND  RUBIDIUM  COMPOUNDS.  By  H.  L.  Wells  ....  71 

ON  SOME  PECULIAR  HALIDES  OF  POTASSIUM  AND  LEAD. 

ByH.  L.Weils 77 

ON  THALLIUM  TRIIODIDE  AND  ITS  RELATION  TO  THE  ALKALI- 
METAL  TRIIODIDES.  By  H.  L.  Wells  and  S.  L.  Penfield  84 

ON  SOME  COMPOUNDS  CONTAINING  LEAD  AND  EXTRA 

IODINE.  By  H.  L.  Wells 89 

ON  THE  VOLUMETRIC  DETERMINATION  OF  TITANIC  ACID 

AND  IRON  IN  ORES.  By  H.  L.  Wells  and  W.  L.  Mitchell  97 

ON  SOME  COMPOUNDS  OF  TRIVALENT  VANADIUM.  By  James 

Locke  and  Gaston  H.  Edwards 103 

ON  AN  ISOMER  OF  POTASSIUM  FfiRRiCYANiDE.  By  James 

Locke  and  Gaston  H.  Edwards 116 

ON  THE  FORMATION  OF  POTASSIUM  £-FERRICYANIDE 
THROUGH  THE  ACTION  OF  ACIDS  UPON  THE  NORMAL 
FERRICYANIDE.  By  James  Locke  and  Gaston  H.  Edwards  130 


x  CONTENTS 

PAPERS    ON   GENERAL    INORGANIC    CHEMISTRY  — 

continued.  PAGE 

ON  THE  SEPARATION  OF  TUNGSTIC  AND  SILICIC  ACIDS.    By 

H.  L.  Wells  and  F.  J.  Metzger 136 

ON  A  SALT  OF  QUADRIVALENT  ANTIMONY.    By  H.  L.  Wells 

and  F.  J.  Metzger 139 

ON  THE  PURIFICATION   OF  CAESIUM  MATERIAL.     By  H.  L. 

'  Wells 142 

ON  THE  ACID  NITRATES.     By  H.  L.  Wells  and  F.  J.  Metzger     146 
INVESTIGATIONS  ON  DOUBLE  NITRATES  : 

I.  CESIUM  DOUBLE  NITRATES.    By  H.  L.  Wells  and  A.  P. 

Beardsley 151 

II.  CAESIUM  BISMUTH  NITRATE.     By  G.  S.  Jamieson    .     .     153 
III.  THALLOUS  THALLIC  NITRATE.     By  F.  J.  Metzger  .     .     154 
ON  CAESIUM  PERIODATE  AND  IODATE-PERIODATE.    By  H.  L. 

Wells 155 

ON  THE  PERIODIC   SYSTEM  AND  THE  PROPERTIES  OF  INOR- 
GANIC COMPOUNDS.     By  James  Locke 158 


PAPERS  ON  DOUBLE  HALOGEN  SALTS: 

ON  SOME  DOUBLE  HALIDES  OF  SILVER  AND  THE  ALKALI 
METALS.  By  H.  L.  Wells  and  H.  L.  Wheeler.  WITH 
THEIR  CRYSTALLOGRAPHY.  By  S.  L.  Penfield  .  .  .  .  207 

ON   THE  CESIUM  AND  RUBIDIUM  CflLORAURATES   AND  BROM- 

AURATES.     By  H.  L.  Wells  and  H.  L.  Wheeler.     WITH 
THEIR  CRYSTALLOGRAPHY.     By  S.  L.  Penfield    .     .     .     .     211 
ON  THE  CAESIUM-MERCURIC  HALIDES.     By  H.  L.  Wells  .     .218 
ON    THE    CRYSTALLOGRAPHY    OF    THE    CAESIUM-MERCURIC 

HALIDES.     By  S.  L.  Penfield 236 

ON   THE   CAESIUM-  AND   THE   POTASSIUM-LEAD   HALIDES.      By 

H.  L.  Wells 250 

ON  THE  DOUBLE  HALIDES  OF  TELLURIUM  WITH  POTASSIUM, 

RUBIDIUM,  AND  CESIUM.  By  H.  L.  Wheeler  ....  268 
ON  THE  AMMONIUM-LEAD  HALIDES.  By  H.  L.  Wells  and 

W.  R.  Johnston 283 

ON  THE  RUBIDIUM-LEAD  HALIDES,  AND  A  SUMMARY  OF  THE 

DOUBLE  HALIDES  OF  LEAD.  By  H.  L.  Wells  ....  295 
ON  THE  DOUBLE  HALIDES  OF  ARSENIC  WITH  CAESIUM  AND 

RUBIDIUM  ;   AND    ON   SOME   COMPOUNDS  OF  ARSENIOUS 

OXIDE  WITH  THE  HALIDES  OF  CJESIUM,  RUBIDIUM,  AND 

POTASSIUM.  By  H.  L.  Wheeler 300 

ON  SOME  DOUBLE  SALTS  OF  LEAD  TETRACHLORIDE.  By 

H.  L.  Wells 313 


CONTENTS  xi 

PAPERS   ON  DOUBLE  HALOGEN   SALTS  —  continued. 

PAGE 
ON  THE  DOUBLE  HALIDES  OF  ANTIMONY  WITH  RUBIDIUM. 

By  H.  L.  Wheeler        320 

ON  THE  DOUBLE   CHLORIDES,  BROMIDES,  AND   IODIDES   OF 

CAESIUM  AND  ZlNC,  AND  OF  CAESIUM  AND  MAGNESIUM. 

By  H.  L.  Wells  and  G.  F.  Campbell 342 

ON   THE   C.ESIUM-CUPRIC    CHLORIDES.     By  H.  L.  Wells  and 

L.  C.  Dupee  . 347 

ON  THE    C^SIUM-CUPRIC    BROMIDES.      By  H.  L.  Wells  and 

P.  T.  Walden 352 

ON  THE  CAESIUM-CUPROUS  CHLORIDES.     By  H.  L.  Wells  .     .     354 
ON  THE  DOUBLE   CHLORIDES   AND   BROMIDES   OF  CAESIUM, 

RUBIDIUM,  POTASSIUM,  AND  AMMONIUM  WITH  FERRIC 

IRON,    WITH  A    DESCRIPTION    OF    Two    FERRO-FERRIC 

DOUBLE  BROMIDES.     By  P.  T.  Walden 357 

ON     THE     CAESIUM-COBALT      AND      C^ESIUM-NlCKEL     DOUBLE 

CHLORIDES,  BROMIDES,  AND  IODIDES.  By  G.  F.  Camp- 
bell  366 

ON  THE  DOUBLE  HALIDES  OF  CAESIUM,  RUBIDIUM,  SODIUM, 

AND  LITHIUM  WITH  THALLIUM.  By  J.  H.  Pratt  .  .  .  370 

ON  THE  DOUBLE  SALTS  OF  CAESIUM  CHLORIDE  WITH  CHRO- 
MIUM TRICHLORIDE  AND  WITH  URANYL  CHLORIDE.  By 
H.  L.  Wells  and  B.  B.  Boltwood 381 

ON  THE  AMMONIUM-CUPROUS  DOUBLE  HALOGEN  SALTS.  By 

H.  L.  Wells  and  E.  B.  Hurlburt 385 

ON  THE  DOUBLE  FLUORIDES  OF  CAESIUM  AND  ZIRCONIUM. 

By  H.  L.  Wells  and  H.  W.  Foote 390 

ON  CERTAIN  DOUBLE  HALOGEN  SALTS  OF  CAESIUM  AND 

RUBIDIUM.  By  H.  L.  Wells  and  H.  W.  Foote  ....  394 

ON  THE  DOUBLE  FLUORIDES  OF  ZIRCONIUM  WITH  LITHIUM, 
SODIUM,  AND  THALLIUM.  By  H.  L.  Wells  and  H.  W. 
Foote 400 

ON  THE  CESIUM  ANTIMONIOUS  FLUORIDES  AND  SOME  OTHER 
DOUBLE  HALIDES  OF  ANTIMONY.  By  H.  L.  Wells  and 
F.  J.  Metzger 407 

ON  THE  DOUBLE  CHLORIDES  OF  CAESIUM  AND  THORIUM. 

By  H.  L.  Wells  and  J.  M.  Willis 415 

ON  A  CJESIUM  TELLURIUM  FLUORIDE.  By  H.  L.  Wells  and 

J.  M.  Willis 418 

GENERALIZATIONS  ON  DOUBLE  HALOGEN  SALTS.  By  H.  L. 

Wells 420 

INDEX  .     443 


SHEFFIELD   LABORATORY. 

THE  Chemical  Department  of  the  Sheffield  Scientific  School 
holds  the  distinction  of  having  been  the  starting-point  of  the 
school.  The  Philosophical  Department  of  Yale  College,  as  it 
was  at  first  called,  formed  its  first  class  in  1847,  using  as  a 
laboratory  the  old  President's  House,  which  stood  on  the 
College  Campus  where  Farnam  Hall  now  stands.  John  P. 
Norton,  Professor  of  Agricultural  Chemistry,  and  Benjamin 
Silliman,  Jr.,  Professor  of  Applied  Chemistry,  were  the  first 
instructors ;  and  among  the  earliest  students  were  G.  J.  Brush, 
W.  H.  Brewer,  and  S.  W.  Johnson,  who  have  been  so  promi- 
nent in  the  development  of  the  school. 

Yale  College  had  taken  an  early  prominence  in  chemistry 
from  the  fact  that  Benjamin  Silliman,  the  elder,  had  begun 
his  labors  here  in  1804.  He  had  just  returned  from  England, 
where  he  had  pursued  chemical  studies  and  had  attended 
lectures  by  John  Dalton,  the  founder  of  the  atomic  theory. 
In  1818  he  founded  the  "  American  Journal  of  Science,"  which 
has  been  published  continuously  to  the  present  time,  and  is 
one  of  the  oldest  scientific  periodicals  in  the  world.  Most  of 
the  publications  from  the  Sheffield  Laboratory  until  recent 
times  have  appeared  in  this  journal. 

The  chemical  laboratory  in  the  old  President's  House  con- 
tinued to  be  used  for  a  period  of  thirteen  years.  Meanwhile 
Professor  Silliman,  the  younger,  had  severed  his  active  con- 
nection with  it,  and  Professor  Norton,  after  a  highly  valued 
service  of  five  years,  had  died  at  the  early  age  of  thirty,  and 
was  succeeded  by  Professor  John  A.  Porter. 

Through  the  liberality  of  Joseph  E.  Sheffield  the  Chemical 
Department,  now  united  to  an  Engineering  Department  which 
had  existed  on  the  College  ground  for  a  number  of  years, 
was  removed  in  1860  to  the  building  now  known  as  Sheffield 


2  SHEFFIELD  LABORATORY. 

Hall.  Here  laboratories  which  were  very  commodious  and 
complete  for  their  day  were  fitted  up,  and  the  Sheffield 
Chemical  Laboratory,  gradually  expanding  as  other  depart- 
ments were  provided  with  new  buildings,  remained  in  this 
place  for  a  period  of  thirty-five  years. 

Professor  Brush  had  been  appointed  to  the  chair  of  Metal- 
lurgy in  1855,  and  S.  W.  Johnson  became  Professor  of  An- 
alytical Chemistry  in  1856,  while  the  laboratory  was  still  in 
the  old  President's  House.  The  entire  charge  of  the  labora- 
tory was  soon  put  into  the  hands  of  these  two  gentlemen. 
Professor  Porter,  who  was  Mr.  Sheffield's  son-in-law,  resigned 
in  1864  on  account  of  ill-health,  and  died  two  years  later. 

The  history  of  the  laboratory  in  Sheffield  Hall  was  one  of 
steady  growth  and  development ;  a  wider  range  of  instruction 
was  gradually  introduced,  and  from  it  have  branched  the 
departments  of  Mineralogy  and  Physiological  Chemistry.  Pro- 
fessor Brush  at  an  early  date  turned  his  attention  to  mineral- 
ogy, which  he  taught  for  many  years,  and  in  which  he  made 
many  important  investigations,  an  account  of  which  appears 
in  another  volume  of  this  series.  He  gradually  gave  up  his 
direct  connection  with  the  Chemical  Department  on  account 
of  his  duties  as  executive  officer  of  the  school. 

Professor  R.  H.  Chittenden  began  instruction  in  physio- 
logical chemistry  in  1875.  From  his  efforts  grew  the  Depart- 
ment of  Physiological  Chemistry  and  Physiology,  which  for 
a  time  was  housed  in  Sheffield  Hall  with  the  chemical  labo- 
ratory, until  in  1889  the  acquisition  of  the  Sheffield  Mansion 
gave  it  independent  quarters. 

Professor  Johnson  paid  particular  attention  to  agricultural 
chemistry,  in  which  he  became  a  leading  authority,  and  con- 
tinued to  teach  this  subject,  as  well  as  organic  and  theoreti- 
cal chemistry,  until  his  retirement  as  Professor  Emeritus  in 
1895. 

From  1871  to  1886  Professor  O.  D.  Allen  took  charge  of 
the  instruction  in  analytical  chemistry  and  metallurgy.  His 
work  with  Professor  Johnson  on  caesium  compounds  and  in 
correcting  Bunsen's  first  determination  of  the  atomic  weight 


SHEFFIELD  LABORATORY.  3 

of  caesium  was  very  important.  Professor  Allen  was  obliged 
to  retire  from  the  school  in  1886  on  account  of  poor  health. 

Professor  Brewer,  who  was  appointed  to  the  chair  of 
Agriculture  at  an  early  date,  took  charge  of  the  instruction  in 
elementary  chemistry  for  a  number  of  years.  Since  1874  this 
instruction  has  been  in  charge  of  Professor  W.  G.  Mixter, 
who  has  also  carried  out  many  investigations,  particularly  in 
the  lines  of  organic  and  physical  chemistry. 

In  1895  the  Chemical  Department  moved  from  Sheffield 
Hall  into  a  new  laboratory,  which  now  affords  the  space 
and  facilities  required  by  its  growth.  This  building,  which 
is  wholly  devoted  to  chemistry,  is  one  hundred  and  twenty- 
nine  feet  long,  seventy-three  feet  wide  in  front,  and  sixty-three 
feet  wide  in  the  rear,  and  has  three  stories  with  a  high 
basement.  The  laboratory  is  finely  equipped  for  work  in 
elementary,  analytical,  organic,  inorganic,  and  physical  chem- 
istry, and  contains  a  large  chemical  library. 

The  present  chemical  force  consists  of  Professor  Mixter, 
who  has  been  mentioned  previously;  the  writer,  who  was 
appointed  as  instructor  in  1884,  and  has  had  charge  of  the 
analytical  chemistry  and  metallurgy  since  Professor  Allen's 
retirement ;  Assistant  Professor  H.  L.  Wheeler,  who  has  under 
his  care  most  of  the  investigations  in  organic  chemistry ;  Mr. 
W.  J.  Comstock,  who  gives  the  greater  part  of  the  class-room 
instruction  in  organic  chemistry ;  Assistant  Professor  P.  T. 
Walden,  who  is  associated  with  Professor  Mixter  in  the  work 
of  instruction  in  elementary  chemistry;  Dr.  James  Locke, 
instructor  in  inorganic  chemistry;  Dr.  Bayard  Barnes,  in- 
structor in  organic  chemistry ;  and  Dr.  H.  W.  Foote,  instruc- 
tor in  physical  chemistry. 


BIBLIOGRAPHY. 

THE  list  given  here  includes  only  the  publications  of  the 
present  officials  of  the  department,  and  of  those  who  have 
worked  under  their  advice.  This  limitation  has  been  made 
because  much  of  the  other  work  has  been  included  in  the 
volume  of  this  series  which  relates  to  mineralogy,  and  because 
some  of  the  remaining  publications  were  somewhat  outside  of 
the  domain  of  pure  chemistry.  The  list  is  limited  also  to  the 
work  which  the  authors  have  done  in  New  Haven. 

On  Willemite  and  Tephroite,  by  W.  G.  Mixter.  Amer.  Jour.  Sci.  (2),  xlvi, 
pp.  230-233  (1868). 

On  the  Estimation  of  Sulphur  in  Coal  and  Organic  Compounds,  by 
W.  G.  Mixter.  Ibid.  (3),  iv,  pp.  90-95  (1872). 

On  Ethylidenargentamine-ethylidenammonium  Nitrate,  by  W.  G.  Mix- 
ter. Ibid.,  xiv,  pp.  195-201  (1877). 

On  Amylidenamine  Silver  Nitrate,  by  W.  G.  Mixter.  Ibid.,  xv,  pp. 
205-208  (1878). 

On  Ethylidenamine  Silver  Sulphate,  by  W.  G.  Mixter.  Ibid.,  xvii,  pp. 
427-429  (1879). 

On  some  Compounds  of  Aromatic  Amines  with  Silver  Nitrate  and  Sul- 
phate, by  W.  G.  Mixter.  Amer.  Chem.  Jour.,  i,  pp.  239-243  (1880). 

On  the  Density  of  the  Vapors  of  some  Ammonium  and  Ammonia  Com- 
pounds, by  W.  G.  Mixter.  Ibid.,  ii,  pp.  153-158  (1881). 

Estimation  of  Sulphur  in  Illuminating  Gas  by  Burning  in  Oxygen.  A 
synthesis  of  water  for  a  lecture  experiment,  by  W.  G.  Mixter.  Ibid., 
pp.  244-247  (1882). 

On  Sauer's  Method  of  estimating  Sulphur,  and  some  Modifications,  by 
W.  G.  Mixter.  Ibid.,  pp.  396-401  (1882). 

On  Urea  from  Ammonia  and  Carbon  Dioxide,  by  W.  G.  Mixter.  Ibid., 
iv,  pp.  35-38  (1882). 

On  some  Reductions  with  Zinc  and  Ammonia,  by  W.  G.  Mixter.  Ibid., 
v,  pp.  1-7 ;  pp.  282-286  (1883). 

On  the  Reduction  of  Benzoyl-orthonitranilide,  by  W.  G.  Mixter.  Ibid., 
vi,  pp.  26-28  (1884). 

Gerhardite  and  Artificial  Basic  Cupric  Nitrates,  by  H.  L.  Wells  and  S.  L. 
Penfield.  Amer.  Jour.  Sci.,  xxx,  pp.  50-57  (1885). 


BIBLIOGRAPHY.  5 

On  New  Acid  Proprionates  and  Butyrates,  by  W.  G.  Mixter.     Amer. 

Chem.  Jour.,  viii,  pp.  343-346  (1886). 
On  Para-form-nitr-anilide,  by  T.  B.  Osborne  and  W.  G.  Mixter.     Ibid., 

pp.  346-347  (1886). 
On  Para-dibrom-ortho-azo-acetanilide,  by  C.  H.  Matthieson  and  W.  G. 

Mixter.     Ibid.,  pp.  347-349  (1886). 
On  Halogen  Derivatives  of  Oxamilide,  by  J.  O.  Dyer  and  W.  G.  Mixter. 

Ibid.,  pp.  349-357  (1886). 
Bismutosphserite  from  Willimantic  and  Portland,  Conn.,  by  H.  L.  Wells. 

Amer.  Jour.  Sci.,  xxxiv,  pp.  221-227  (1887). 
Basic  Lead  Nitrates,  by  A.  J.  Wakeman  and  H.  L.  Wells.     Amer.  Chem. 

Jour.,  ix,  pp.  229-303  (1887). 
Basic   Zinc   and   Cadmium  Nitrates,  by  H.  L.    Wells.     Ibid.,  ix,  pp. 

304-308   (1887). 
On  Nitro  Derivatives  of  Oxanilide,  by  W.  G.  Mixter  and  F.  O.  Walther. 

Ibid.,  ix,  pp.  355-361  (1887). 
On  Nitro  Derivatives  of  Dibrom-oxanilide,  by  W.  G.  Mixter  and  C.  P. 

Willcox.     Ibid.,  pp.  361-364  (1887). 
Sperrylite,  a  New  Mineral,  by  H.  L.  Wells.     Amer.  Jour.  Sci.,  xxxvii, 

pp.  67-73  (1889). 
Description  of  the  New  Mineral,  Beryllonite,  by  E.  S.  Dana  and  H.  L. 

Wells.     Ibid.,  xxxvii,  pp.  23-32  (1889). 
An  Elementary  Text-Book  of  Chemistry,  by  W.  G.  Mixter.    8°,  viii  +  459 

pp.      New  York,  1889.    [The  part  on  Physics  of  Chemistry,  pp.  1-45, 

and  Spectral  Analysis,  pp.  90-94,  is  by  C.  S.  Hastings.] 
On  Nitro  Derivatives  of  Oxaltoluide,  by  W.  G.  Mixter  and  F.  Kleeberg. 

Amer.  Chem.  Jour.,  xi,  pp.  236-240  (1889). 
Analyses  of  Several  Manganesian  Phosphates,  by  H.  L.  Wells.     Amer. 

Jour.  Sci.,  xxxix,  pp.  201-216  (1890). 
On  some  Selenium  and  Tellurium  Minerals  from  Honduras,  by  E.  S. 

Dana  and  H.  L.  Wells.     Ibid.,  xl,  pp.  78-82  (1890). 
On  Silver  Formanilide,  by  W.  J.  Comstock  and  F.  Kleeberg.     Amer. 

Chem.  Jour.,  xii,  pp.  493-502  (1890). 
On  the  Composition  of  Pollucite  and  its  Occurrence  at  Hebron,  Maine, 

by  H.  L.  Wells.     Amer.  Jour.  Sci.,  xli,  pp.  213-220  (1891). 
On   a  Self -feeding    Sprengel   Pump,  by  H.   L.  Wells.      Ibid.,  xli,  pp. 

390-394  (1891). 
Researches  on  the  Isoanilides,  by  W.  J.  Comstock  and  H.  L.  Wheeler. 

Amer.  Chem.  Jour.,  xiii,  p.  514  (1891). 

On  the   Preparation   of  the    Oxygen  Ethers  Succinimide  from  its  Sil- 
ver Salt,  by  W.  J.   Comstock  and  H.  L.  Wheeler.      Ibid.,  p.  520 

(1891). 
On  some  Derivatives  of  Aromatic  Formyl  Compounds,  by  W.  J.  Comstock 

and  R.  R.  Clapp.    Ibid.,  p.  524  (189i). 


6  BIBLIOGRAPHY. 

On  a  Series  of  Caesium  Trihalides,  by  H.  L.  Wells.     Including  their 

crystallography,  by  S.  L.  Penfield.     Amer.  Jour.  Sci.,  xliii,  pp.  17-32 

(1892). 
On  the  Rubidium  and  Potassium  Trihalides,  by  H.  L.  Wells  and  H.  L. 

Wheeler.     With  their  crystallography,  by  S.  L.  Penfield.     Ibid.,  xliii, 

pp.  476-487  (1892). 
On  the  Alkali-metal  Pentahalides,  by  H.  L.  Wells  and  H.  L.  Wheeler. 

With  their  crystallography,  by  S.  L.  Penfield.     Ibid.,  xliv,  pp.  42-49 

(1892). 
On  Herderite  from  Hebron,  Maine,  by  H.  L.  Wells  and  S.  L.  Penfield. 

Ibid.,  xliv,  pp.  114-116  (1892). 
On  some  Double  Halides  of  Silver  and  the  Alkali-metals,  by  H.  L.  Wells 

and  H.  L.  Wheeler.     W^ith  their  crystallography,  by  S.  L.  Penfield. 

Ibid.,  xliv,  pp.  155-157  (1892). 
On  the  Caesium  and  Rubidium  Chloramates  and  Bromamates,  by  H.  L. 

Wells  and  H.  L.   Wheeler.     Writh  their  crystallography,  by  S.  L. 

Penfield.     Ibid.,  xliv,  pp.  157-162  (1892). 
On  some  Alkaline  lodates,  by  H.  L.  W'heeler.     With  crystallographic 

Notes,  by  S.  L.  Penfield.     Ibid.,  xliv,  pp.  124-132  (1892). 
On  the   Caesium-Mercuric   Halides,  by  H.  L.    Wells.     Ibid.,   xliv,   pp. 

221-236  (1892). 
On  the  Caesium-Lead  and  the  Potassium-Lead  Halides,  by  H.  L.  Wells. 

Ibid.,  xlv,  pp.  121-134  (1893). 
On  the  Double  Halides  of  Tellurium  with   Potassium,  Rubidium,  and 

Caesium,  by  H.  L.  Wheeler.     Ibid.,  xlv,  pp.  267-269  (1893). 
On  the  Ammonium-Lead  Halides,  by  H.  L.  Wells  and  W.  R.  Johnston. 

Ibid.,  xlvi,  pp.  25-34  (1893). 
On  the  Rubidium-Lead  Halides,  and  a  Summary  of  the  Double  Halides 

of  Lead,  by  H.  L.  Wells.     Ibid.,  xlvi,  pp.  34-38  (1893). 
On  the  Double  Halides  of  Arsenic  with  Caesium  and  Rubidium ;  and  on 

some  Compounds  of  Arsenious  Oxide  with  the  Halides  of  Caesium, 

Rubidium,  and  Potassium,  by  H.  L.  Wheeler.     Ibid.,  xlvi,  pp.  88-98 

(1893). 
On  the  Deportment  of  Charcoal  with  the  Halogens,  Nitrogen,  Sulphur, 

and  Oxygen,  by  W.  G.  Mixter.     Ibid.,  pp.  363-369  (1893). 
On  some  Double  Salts  of  Lead  Tetrachloride,  by  H.  L.  Wells.     Ibid., 

xlvi,  pp.  180-186  (1893). 
On  a  Method  for  the  Quantitative  Determination  of  Caasium,  and  the 

Preparation  of   Pure  Caesium  and  Rubidium  Compounds,  by  H.  L. 

Wells.     Ibid.,  xlvi,  pp.  186-190  (1893). 
On  some  Peculiar  Halides  of  Potassium  and  Lead,  by  H.  L.  Wells.     Ibid., 

xlvi,  pp.  190-195  (1893). 
On  the  Double  Halides  of  Antimony  with  Rubidium,  by  H.  L.  Wheeler. 

Ibid.,  xlvi,  pp.  269-279  (1893). 


BIBLIOGRAPHY.  1 

On  the  Double  Chlorides,  Bromides,  and  Iodides  of  Caesium  and  Cad- 
mium, by  II.  L.  Wells  and  P.  T.  Walden.     Amer.  Jour.  Sci.,  xlvi, 

pp,  425-431  (1893). 
On  the  Double  Chlorides,  Bromides,  and  Iodides  of  Caesium  and  Zinc, 

and  of  Caesium  and  Magnesium,  by  H.  L.  Wells  and  G.  F.  Campbell. 

Ibid.,  pp.  431-434  (1893). 
On  the  Caesium-Cupric  Chlorides,  by  H.  L.  Wells  and  L.  C.  Dupee.  Ibid., 

xlvii,  pp.  91-93  (1894). 
On  the  Csesium-Cupric  Bromides,  by  H.  L.  Wells  and  P.  T.  Walden. 

Ibid.,  xlvii,  pp.  94-96  (1894). 
On  the  Caesium-Cuprous  Chlorides,  by  H.  L.  Wells.     Ibid.,  xlvii,  pp. 

96-98  (1894). 
On  Thallium  Triiodide  and  its  Relation  to  the  Alkali-Metal  Triiodides, 

by  H.  L.  Wells  and  S.  L.  Penfield.     Ibid.,  xlvii,  pp.  463-466  (1894). 
On  the  Occurrence  of  Leadhillite  in  Missouri  and  its  Chemical  Composi- 
tion, by  L.  V.  Pirsson  and  H.  L.  Wells.     Ibid.,  xlviii,  pp.  219-226 

(1894). 
On  the  Double  Chlorides  and  Bromides  of  Caesium,  Rubidium,  Potassium, 

and  Ammonium  with  Ferric  Iron,  with  a  Description  of  two  Ferro- 

ferric  double  bromides,  by  P.  T.  Walden.      Ibid.,  xlviii,  pp.  283-290 

(1894). 
On  the  Caesium-Cobalt  and  Caesium-Nickel  Double  Chlorides,  Bromides, 

and  Iodides,  by  G.  F.  Campbell.     Ibid.,  xlviii,  pp.  418-420  (1894). 
On  some  Azo  and  Azimido  Compounds,  by  W.  G.  Mixter.     Amer.  Chem. 

Jour.,  xvii,  pp.  449-453  (1895). 
On  the  Double  Halides  of   Caesium,  Rubidium,  Sodium,  and  Lithium 

with  Thallium,  by  J.  II.  Pratt.     Amer.  Jour.  Sci.,  xlix,  pp.  397-404 

(1895). 
On  some  Compounds  containing  Lead  and  Extra  Iodine,  by  H.  L.  Wells. 

Ibid.,  1,  pp.  21-26  (1895). 
On  the  Double  Salts  of  Caesium  Chloride  with  Chromium  Trichloride, 

and  with  Uranyl  Chloride,  by  H.  L.  Wells  and  B.  B.  Boltwood.   Ibid., 

1,  pp.  249-252  (1895). 
On  the  Ammonium-Cuprous  Double  Halogen  Salts,  by  H.  L.  Wells  and 

E.  B.  Hurlburt.     Ibid.,  1,  pp.  390-393  (1895). 
On  the  Volumetric  Determination  of  Titanic  Acid  and  Iron  in  Ores,  by 

H.  L.  Wells  and  W.  L.  Mitchell.     Jour.  Amer.  Chem.  Soc.,  xvii,  pp. 

878-883  (1895). 
On  the  Double  Fluorides  of  Caesium  and  Zirconium,  by  H.  L.  Wells  and 

H.  W.  Foote.     Amer.  Jour.  Sci.  (4),  i,  pp.  18-20  (1896). 
On  Halogen  Addition-Products  of  the  Anilides,  by  H.  L.  Wheeler  and 

P.  T.  Walden.     Amer.  Chem.  Jour.,  xviii,  p.  85  (1896). 
The  Action  of  Acid  Chlorides  on  the  Silver  Salts  of  the  Anilides,  by 

H.  L.  Wheeler  and  B.  B.  Boltwood.     Ibid.,  xviii,  p.  381  (1896). 


8  BIBLIOGRAPHY. 

On  some  Mercury  Salts  of  the  Anilides,  by  H.  L.  Wheeler  and  B.  W. 

McFarland.     Amer.  Chem.  Jour.,  xviii,  p.  540  (1896). 
On  the  Use  of  Antimony  Trichloride  in  the  Synthesis  of  Aromatic  Ketones 

by  W.  J.  Comstock.     Ibid.,  pp.  547-552  (1896). 
On  Diacid  Anilides,  by  H.  L.  Wheeler.     Ibid.,  xviii,  p.  695  (1896). 
On  the  Action  of  Acid  Chlorides  on  the  Imido  Esters  and  Isoanilides  and 

on  the  Structure  of  the  Silver  Salts  of  the  Anilides,  by  H.  L.  Wheeler 

and  P.  T.  Walden.     Ibid.,  xix,  p.  129  (1897). 
On  the  Action  of  Chlorcarbonic  Ethyl  Ester  on  Formanilide,  by  H.  L. 

Wheeler  and  H.  F.  Metcalf.     Ibid.,  xix,  p.  217  (1897). 
On  the  Preparation  of  Metabrombenzoic  Acid  and  of  Metabromnitro- 

benzene,  by  H.  L.  Wheeler  and  B.  W.  McFarland.     Ibid.,  xix,  p.  363 

(1897). 
On  the  Non- Existence  of  Four  Methenylphenylparatolyl  Amidines,  by 

H.  L.  Wheeler.     Ibid.,  xix,  p.  365  (1897). 
On  the  Molecular  Rearrangement  of  the  Oxines  by  Means  of  Certain 

Metallic  Salts,  by  W.  J.  Comstock.     Ibid.,  xix,  pp.  485-492  (1897). 
On  Electrosynthesis,  by  W.  G.  Mixter.     Amer.  Jour.  Sci.,  iv,  pp.  51-62 

(1897). 
On  Halogen  Addition  Products  of  the  Anilides,  by  H.  L.  Wheeler,  Bayard 

Barnes,  and  J.  H.  Pratt.     Amer.  Chem.  Jour.,  xix,  p.  672  (1897). 
On  Diacyl  Anilides,  by  H.  L.  Wheeler,  T.  E.  Smith,  and  C.  H.  Warren. 

Ibid.,  xix,  p.  757  (1897). 
Fresenius's  Manual  of  Qualitative  Chemical  Analysis.     Translated  by 

H.  L.  Wells.     8vo,  pp.  xvii,  748  (Xew  York,  1897). 
On  Certain  Double  Halogen  Salts  of  Caesium  and  Rubidium,  by  H.  L. 

Wells  and  H.  W.  Foote.     Amer.  Jour.  Sci.,  iii,  pp.  461-465  (1897). 
On  the  Double  Fluorides  of  Zirconium  with  Lithium,  Sodium,  and  Thal- 
lium, by  H.  L.  Wells  and  H.  W.  Foote.     Ibid.,  iii,  pp.  466-471  (1897). 
On  Acylimidoesters,  by  H.  L.  Wheeler,  P.  T.  Walden,  and  H.  F.  Metcalf. 

Amer.  Chem.  Jour.,  xx,  p.  64  (1898). 
Note  on  Double  Salts  of  the  Anilides  with  Cuprous  Chloride  and  Cuprous 

Bromide,  by  W.  J.  Comstock.     Ibid.,  pp.  77-79  (1898). 
On    some    Bromine    Derivatives    of    2-3-Dimethylbutane,    by    H.    L. 

Wheeler.     Ibid.,  xx,  148  (1898). 
On  the  Silver  Salt  of  4-Nitro-2-Arainobenzoic  Acid  and  its  Behavior  with 

Alkyl  and   Acyl   Halides,  by  H.  L.  Wheeler  and  Bayard   Barnes. 

Ibid.,  xx,  217  (1898). 
On  the  Action  of  Hydrogen  Sulphide  upon  Vanadates,  by  James  Locke. 

Ibid.,  xx,  pp.  373-376  (1898). 
Researches  on   the   Cycloamidines :    Pyrimidine   Derivatives,  by  H.  L. 

Wheeler.     Ibid.,  xx,  481  (1898). 
A  Laboratory  Guide  in  Qualitative  Chemical  Analysis,  by  H.  L.  Wells, 

8vo,  pp.  vi,  189  (New  York,  1898). 


BIBLIOGRAPHY.  9 

Researches  on  the  Cycloamides :  a-Ketobenzmorpholine  and  a-Benzpara- 

oxazine  Derivatives,  by  H.  L.  Wheeler  and  Bayard  Barnes.     Amer. 

Chem.  Jour.,  xx,  555  (1898). 
The  Action  of  Amines  on  Acylimido  Esters :  Acyl  Amidines,  by  H.  L. 

Wheeler  and  P.  T.  Walden.     Ibid.,  xx,  568  (1898). 
On  the  Periodic  System  and  the  Properties  of  Inorganic  Compounds,  by 

James  Locke.     Ibid.,  xx,  pp.  581-592  (1898). 
The  Action   of  Sulphur  upon  Metallic   Sodium,  by  James  Locke   and 

Alfred  Austell.     Ibid.,  xx,  pp.  592-594  (1898). 
On  some  Compounds  of  Trivalent  Vanadium,  by  James  Locke  and  G. 

H.  Edwards.     Ibid.,  xx,  594-606  (1898). 
On  Electrosynthesis  (Second  Paper),  by  W.  G.  Mixter.     Amer.  Jour.  Sci., 

vi,  pp.  217-224  (1898). 
On  the   Non-Existence  of   Four   Methenylphenylparatolylamidines,   by 

H.  L.  Wheeler  and  T.  B.  Johnson.    Amer.  Chem.  Jour.,  xx,  853  (1898). 
On  the  Rearrangement  of  Imidoesters,  by  H.  L.  Wheeler  and  T.  B. 

Johnson.     Ibid.,  xxi,  185  (1899). 
On  an  Isoiner  of  Potassium  Ferricyanide,  by  James  Locke  and  G.  H. 

Edwards.     Ibid.,  xxi,  pp.  193-206  (1899). 
On  the  Formation  of  Potassium  /3-Ferricyanide  through  the  Action  of 

Acids  upon  the  Normal  Ferricyanide,  by  James  Locke  and  G.  H. 

Edwards.    Ibid.,  xxi,  pp.  413-418  (1899). 
On  some  Experiments  with  Endothermic  Gases,  by  W.  G.  Mixter.     Amer. 

Jour.  Sci.,  vii,  pp.  323-327  (1899). 
On  a  Hypothesis  to  Explain  the  Partial  Non-Explosive  Combination  of 

Explosive  Gases  and  Gaseous  Mixtures,  by  W.  G.  Mixter.     Ibid.,  pp. 

327-334  (1899). 
On  the  Rearrangement  of  the  Thioncarbamic  Esters,  by  H.  L.  Wheeler 

and  Bayard  Barnes.     Amer.  Chem.  Jour.,  xxi,  141  (1899). 
Researches  on   Substitution :    the  Action    of    Bromine  on  Metachlor-, 

metabrom-,   and  metaiodanilines,  by   H.   L.  Wheeler  and  William 

Valentine.     Ibid.,  xxii,  266  (1899). 
On  the  Products  of  Explosion  of  Acetylene,  by  W.  G.  Mixter.     Amer. 

Jour.  Sci.,  ix,  pp.  1-8  (1900). 
On  the  Rearrangement  of  Imidoesters  (Second  Paper),  by  H.  L.  Wheeler. 

Arner.  Chem.  Jour.,  xxiii,  135  (1900). 
Researches  on  the  Sodium  Salts  of  the  Amides,  by  H.  L.  Wheeler.     Ibid., 

xxiii,  453  (1900). 
On    the    Molecular    Rearrangement   of  the  Thioncarbamic,    Thioncar- 

banilic,  and  Thioncarbazinic  Esters  :  /3-Alkyl-a-/t-Diketotetrahydrothi- 

azoles,  by  H.  L.  Wheeler  and  Bayard  Barnes.     Ibid.,  xxiv,  60  (1900). 
On  Ureaimido  Esters,  Thioureaimido  Esters,  Acylthioureaimido  Esters, 

and    Ureaamidines,   by   H.    L.   Wheeler   and   W.   Murray    Sanders. 

Jour.  Amer.  Chem.  Soc.,  xxii,  365  (1900). 


10  BIBLIOGRAPHY. 

On  the  Behavior  of  Acylthioncarbamic  Esters  towards  Alkyl  Iodides 

and  Amines :  Benzoylimidothiocarbonic  Esters,  Acyclic  Benzoylpseu- 

doureas  and  Benzoylureas,  by  H.  L.  Wheeler  and  T.  B.  Johnson. 

Am.  Chem.  Jour.,  xxiv,  189  (1900). 
On  the  Products  of  the  Explosion  of  Acetylene,  and  of  Mixtures  of 

Acetylene  and  Nitrogen  (Second  Paper),  by   W.  G.  Mixter.     Am. 

Jour.  Sci.,  x,  pp.  299-309  (1900). 
On  the  Molecular  Rearrangement  of  Disubstituted  Thioncarbamic  Ester : 

Phenylimidocarbonic  Acid  Derivatives  and  Thiosemicarbazidic  Esters, 

by  H.  L.  Wheeler  and  Guy  K.  Dustin.     Ibid.,  xxiv,  424  (1900). 
On  the  Action  of  Alkylthiocyanates  and  Alkylisothiocyanates  with  Thiol- 

Acids,  by  H.  L.  Wheeler  and  H.  F.  Merriam  * 
On  Acetyl  and   Benzoylmidodithiocarbonic   Esters,  by  H.  L.  Wheeler 

and  T.  B.  Johnson.* 

Kesearches  on  Thiocyanates  and  Isothiocyanates,  by  H.  L.  Wheeler.* 
On  some  Acetyl  and  Benzoylpseudothioureas,  by  H.  L.  Wheeler  and 

T.  B.  Johnson.* 
On  some  Addition  Reactions  of  Thio  Acids,  by  H.  L.  Wheeler  and 

Bayard  Barnes.* 
On  the  Caesium  Antimonious  Fluorides  and  some  other  Double  Halides 

of  Antimony,  by  H.  L.  Wells  and  F.  J.  Metzger.* 
On  the  Separation  of  Tungstic  and  Silicic  Acids,  by  H.  L.  Wells  and 

F.  J.  Metzger.* 

On  a  Salt  of  Quadrivalent  Antimony,  by  H.  L.  Wells  and  F.  J.  Metzger.* 
On  the  Purification  of  Caesium  Material,  by  H.  L.  Wells.* 
On  the  Acid  Nitrates,  by  H.  L.  Wells  and  F.  J.  Metzger.* 
Investigations  on  Double  Nitrates  :  I.  Caesium  Double  Nitrates,  by  H.  L. 

Wells  and  A.  P.  Beardsley ;  II.  Caesium  Bismuth  Nitrate,  by  G.  J. 

Jamieson ;  III.  Thallous  Thallic  Nitrate,  by  F.  J.  Metzger  * 
On  Caesium  Periodate  and  lodate-Periodate,  by  H.  L.  Wells.* 
On  the  Double  Chlorides  of  Caesium  and  Thori^un,  by  H.  L.  Wells  and 

J.  M.  Willis.* 

On  a  Csesium  Tellurium  Fluoride,  by  H.  L.  Wells  and  J.  M.  Willis.* 
On  the  Periodic  System  and  the  Properties  of  Inorganic  Compounds  :  II. 

Gradations  in  the  Properties  of  Alums,  by  James  Locke.* 
On  the  Periodic  System  and  the  Properties  of  Inorganic  Compounds: 

III.  The  Solubilities  of  Alums  as  a  Function  of  Two  Variables,  by 

James  Locke.* 
Generalizations  on  Double  Halogen  Salts,  by  H.  L.  Wells.* 

*  To  be  published. 


PAPERS  ON 
GENERAL  INORGANIC  CHEMISTRY 


ON  A  SERIES  OF  OESIUM  TRIHALIDES.* 

BY  H.  L.  WELLS. 

INCLUDING  THEIR  CRYSTALLOGRAPHY. 
BY  S.  L.  PENFIELD. 

IN  the  course  of  some  experiments  with  caesium  compounds, 
bromine  was  added  to  a  concentrated  solution  of  caesium  chlo- 
ride with  an  astonishing  result.  There  was  instantly  formed 
a  bright  yellow  precipitate,  so  dense  as  to  nearly  solidify  the 
liquid.  The  substance  readily  dissolved  on  warming  the 
liquid,  and,  on  cooling  it,  large  crystals  of  a  yellowish-red 
color  were  formed  which  were  found  to  be  CsClBr2. 

In  view  of  the  fact  that  KI3  was  already  known,  f  this  dis- 
covery made  it  probable  that  a  series  of  caesium  trihalides 
could  be  obtained.  An  attempt  was  accordingly  made  to 
prepare  each  of  the  following  possible  members  of  such  a 
series  containing  chlorine,  bromine,  and  iodine. 

1.  CsI3  6.   CsCl2I 

2.  CsBrI2  7.    CsBr3 

3.  CsBr2I  8.   CsClBr2 

4.  [CsClI,  9.    CsCl2Br 

5.  CsClBrI  10.   [CsCl,] 

As  a  result,  all  the  members  of  the  series  except  the  two 
enclosed  in  brackets  were  isolated. 

These  eight  trihalides  are  easily  made,  being  much  less 
soluble  than  the  normal  halides.  They  crystallize  beautifully, 
have  remarkably  brilliant  colors,  and  some  of  them  possess  an 
unexpected  degree  of  stability. 

*  Amer.  Jour.  Sci.,  xliii,  January,  1892. 

t  Jorgensen,  J.  pr.  Ch.,  II,  ii,  357  ;  Johnson,  J.  Chem.  Soc.,  1877,  249. 


14  ON  A   SERIES   OF 

Method  of  Preparation. 

Each  of  these  compounds  can  be  made  by  dissolving,  with 
the  aid  of  heat,  the  appropriate  normal  csesium  halide  and 
the  halogen  or  halogens  indicated  by  the  formula  in  the  proper 
amount  of  water,  or,  in  the  single  case  of  CsBrI2,  in  weak 
alcohol,  and  cooling  to  crystallization.  The  caesium  salt  used 
in  making  the  mixed  trihalides  is  preferably  the  one  which 
is  not  decomposed  by  the  halogen  or  halogens  added.  In 
most  cases  the  presence  of  an  excess  of  the  normal  halide  is 
desirable  in  order  that  the  halogens,  especially  iodine,  may 
readily  dissolve  and  not  separate  again  on  cooling,  but 
the  same  result  may  also  be  obtained  by  the  use  of  weak 
alcohol.  Details  of  preparation  will  be  given  for  each  body 
separately. 

Color. 

In  the  following  list  the  compounds  are  arranged  in  order, 
from  the  darkest  to  the  lightest.  The  colors  given,  unless 
otherwise  specified,  are  for  crystals  of  considerable  size,  for 
when  the  bodies  are  obtained  as  precipitates,  or  when  the 
crystals  are  pulverized,  they  are  lighter  in  color. 

CsI3  Brilliant  black,  nearly  opaque  ;  powder  brown. 

CsBrI2        Dark  reddish-brown;  thin  crystals  transmit 

deep  red  light ;  powder  dark  red. 
CsBr2I        Deep  cherry-red. 

£  g          I  Yellowish-red,  each  having  a  somewhat 
C  GIB      j      yellower  tint  than  the  one  preceding  it. 

(  Orthorhombic  variety,  deep  orange. 
82        (  Rhombohedral  variety,  pale  orange. 
CsCl2Br      Bright  yellow. 

Stability  on  Exposure. 

The  five  bodies  containing  iodine  are  much  more  stable 
than  the  others,  and  will  bear  long  exposure  to  the  air  at 
ordinary  temperatures  with  very  slight  superficial  change. 
This  exposure  in  some  cases  may  be  continued  for  a  week  or 


CESIUM  TRIHALIDES.  15 

more  in  warm  weather  without  producing  any  marked  alter- 
ation of  color,  but  they  constantly  give  off  a  slight  odor  and 
finally  begin  to  whiten.  The  three  compounds  containing 
no  iodine  usually  become  white  in  a  few  hours  on  exposure, 
but  even  these  can  be  preserved  indefinitely  in  tightly  corked 
tubes.  Experiments  showed  that  CsBrI2  whitened  more 
rapidly  than  CsBr2I,  also  that  CsClBr2  decomposed  more 
rapidly  than  CsCl2Br.  This  indicates  that  their  stability 
does  not  entirely  depend  upon  the  volatility  of  the  halogens 
contained  in  them,  —  a  point  which  has  a  bearing  on  the  con- 
stitution of  this  group  of  bodies,  and  which  will  be  considered 
subsequently. 

Behavior  when  Heated. 

The  following  table  shows  the  temperatures  of  complete 
decomposition  as  determined  by  the  change  of  color  to  white. 
They  are  only  approximate,  since  they  represent  gradual 
changes  which  vary  somewhat  with  the  rapidity  of  heating. 
The  melting-points  are  also  given.  In  open  tubes  these  are 
usually  sharp,  but  in  sealed  tubes  often  very  gradual. 

Melts  Melts  Becomes  white 

in  open  tube.  in  sealed  tube.  in  open  tube. 

(uncorr.)  (uncorr.)  (approximate.) 

CsI8  210°  201°-208°  330° 

CsBr2I  246°  243°-248°  320° 

CsClBrI  238°  225°-235°  290° 

CsCl2I  238°  225° -230°  290° 

CsBrI2  208°  155°-190°  260° 

CsBr8  whitens  180°  160° 

CsCl2Br  whitens  205°  150° 

CsClBr,  whitens  191°  150° 

Behavior  with  Solvents. 

All  these  bodies  except  CsBrI2,  which  is  almost  completely 
decomposed  by  water,  can  be  recrystallized  by  treating  with 
warm  water  and  cooling  the  solution.  There  is  usually  some 
decomposition  during  this  operation,  accompanied  by  the 
separation  of  iodine  or  the  volatilization  of  this  or  the  other 
halogens. 


16  ON  A    SERIES  OF 

All  the  trihalides  containing  iodine  can  be  dissolved  in 
alcohol  and  recrystallized  from  it.  There  is  usually  a  slight 
deposition  of  normal  halide  at  the  same  time,  which  can  be 
avoided  by  adding  a  little  water  to  the  alcohol.  CsI3  is  much 
more  soluble  in  alcohol  than  in  water.  The  other  iodine  com- 
pounds, with  the  exception  of  CsBrI2,  which  decomposes  with 
water,  are  apparently  more  soluble  in  water.  Those  bodies 
containing  no  iodine  are  all  decomposed  by  alcohol,  leaving 
a  white  residue.  Mixtures  of  alcohol  and  water  are  good  sol- 
vents for  all  the  trihalides. 

Ether  has  no  immediate  action  on  the  more  stable  com- 
pounds, CsI8,  CsBr2I,  CsClBrI,  and  CsClJ,  but  it  decomposes 
all  the  others  with  separation  of  normal  halides.  When 
CsBrI2  is  thus  decomposed,  pure  CsBr  is  left. 

Crystallograp  Jiy. 

The  crystallization  of  the  caesium  trihalides  is  orthorhom- 
bic.  The  salts  form  an  isomorphous  group,  the  chief  features 
of  which  will  first  be  given,  followed  by  a  brief  description 
of  the  different  individuals. 

The  forms  which  have  been  observed  are : 

a,  100,  i-1  g,  012,  £-T 

b,  010,  i-i  d,  Oil,  1-T 

c,  001,    0  /,   021,  2-i 
m,  110,    /  e,    102,  \-1 

Of  these  m,  c?,  and  e  are  the  most  prominent  and  usually 
determine  the  habit  of  the  crystals.  Either  m  or  d  usually 
predominates  to  such  an  extent  that  the  crystals  are  prismatic 
in  the  direction  of  the  vertical  or  the  brachy-axes.  The  dome 
/  is  very  common,  but  is  usually  too  small  to  give  a  character- 
istic habit,  and  is  therefore  omitted  from  most  of  the  figures. 
The  face  g  was  observed  only  on  CsI8.  The  pinacoids  are 
variable  in  their  development,  but  commonly  one,  and  fre- 
quently all  three,  can  be  found  on  a  single  crystal.  Pyram- 
idal faces  are  practically  wanting.  In  the  examination  of 
a  great  many  crystals,  but  one  was  found  (of  CsBr2I)  on 


CJ2SIUM  TR1HALIDES. 


17 


which  a  single  pyramidal  face  occurred ;  this  replaced  the  edge 
between  m  and  d,  and  had  the  symbol  132,  f  —  3.  The  cleav- 
age is  perfect,  parallel  to  <?. 

An  idea  of  the  similarity  of  the  different  salts  may  be 
obtained  from  the  following  table,  in  which  the  axial  ratios  * 
and  three  of  the  prominent  angles  are  given.  The  angles 
which  were  chosen  as  fundamental  are  marked  by  an  asterisk, 
the  others  are  calculated,  and  in  all  cases  the  measurements 
showed  close  agreement. 


i 

a:b: 

c 

fCsI3         0.6824:1 

1.1051 

Series 
with  iodine 

CsBrI2    0.6916  :  1 
^  CsBr2I     0.7203  :  1 
CsClBrI  0.7230  :  1 

1.1419 
1.1667 
1.1760 

I  CsCl2I      0.7373  :  1 

1.1920 

Series 
without  iodine 

,  CsBr8       0.6873  :  1 
]  CsClBr2  0.699    :  1 
<CsCl2Br  0.7186:1 

1.0581 
1.1237 

nt  A  m,  110  A  HO 

dAd,  Oil  A  Oil. 

e  A  e,  102  A  T02. 

CsI3 
CsBrI2 
CsBrJ 

*68°  37' 
*69°  20' 
*71°  32' 

*95°  43' 
97°  34' 

*98°  48' 

78°    0' 
*79°    5' 
78°    0' 

CsClBrI 

*71°  44' 

*99°  15' 

78°  15' 

CsCl2I 
CsBr3 

CsClBr2 
CsCl2Br 

72°  48' 
*69°    0' 
*69°  56' 
*71°  24' 

*100°    1' 
*93°  14' 

*96°  40' 

*77°  54' 
*75°  10' 

76°    0' 

CsI8  and  CsBrs  are  almost  identical  in  axial  ratios,  but  it 
is  surprising  that  the  chemically  intermediate  compounds, 
CsBrI2  and  CsBr2I,  are  not  crystallographically  intermediate. 

A  very  remarkable  relation  exists  between  the  first  five 
compounds  in  the  table,  all  of  which  contain  iodine  and  are 

*  The  ratios  are  given  in  two  ways :  I,  with  6  as  unity,  as  is  customary  ; 
and  II,  with  a  as  unity,  in  order  to  show  more  clearly  the  relation  between  d 
and  c. 

2, 


18  ON  A    SERIES   OF 

arranged  in  the  order  of  their  molecular  weights.  The  ratio 
of  two  axes  remains  nearly  constant  throughout,  while  the 
third  varies.*  Exactly  the  same  relation  exists  between  the 
three  compounds  containing  no  iodine,  but  in  this  series 
the  ratio  between  the  two  constant  axes  varies  slightly  from 
the  corresponding  ratio  in  the  iodine  compounds. 

If  an  arrangement  according  to  molecular  weights  is  made 
with  all  the  compounds  containing  bromine,  or  in  like  manner 
with  all  those  containing  chlorine,  a  symmetrical  series  of  axial 
ratios  is  not  formed.  This  leads  to  the  conclusion  that  the 
two  series  given  in  the  table  have  a  special  significance,  and 
that  iodine,  with  the  highest  atomic  weight,  plays  an  important 
part  in  the  constitution  of  the  first,  while  bromine  acts  in  the 
same  way  in  the  second.  Since  several  of  the  compounds  con- 
tain only  a  single  halogen  atom  of  highest  atomic  weight,  it 
follows  that  a  single  atom  throughout  exerts  an  influence  on 
the  symmetry  of  the  series.  This  peculiar  part  played  by  an 
iodine  or  bromine  atom  may  be  explained  by  supposing  it  to  be 
closely  united  either  with  the  caesium  or  with  one  of  the  other 
halogen  atoms.  It  seems  probable  from  these  considerations 
that  the  three  halogen  atoms  in  these  compounds  do  not  have 
similar  positions  in  the  molecule,  and  consequently  that  the 
trihalides  are  not  compounds  of  trivalent  caesium  but  have 
some  other  structure. 

Csls.  —  Of  this  salt,  crystals  from  both  aqueous  and  alco- 
holic solutions  were  examined.  On  the  former  the  forms  «,  e, 
w,  d,  and  /  were  observed.  The  habit  was  different  from  any- 
thing else  in  the  series,  being  needle-like,  with  a  and  m  in  the 
prismatic  zone,  terminated  by  d,  Fig.  1,  or  by  <?,  c?,  and/,  Fig. 
2.  The  crystals  did  not  give  very  satisfactory  reflections,  but 
the  best  measurements,  from  a  number  of  selected  crystals, 
agreed  closely  with  those  given  in  the  table.  The  crystals 
examined  were  20-30  mm.  in  length  and  seldom  over  2  mm. 
in  diameter.  On  the  crystals  from  alcohol,  the  forms  #,  5,  c, 
m,  g,  d,f,  and  e  were  observed.  The  habit  is  shown  in  Fig.  3. 

*  Several  series  of  organic  compounds  with  analogous  axial  relations  have 
been  observed  by  Groth  (Berichte,  iii,  449)  and  by  Hintze  (Berichte,  vi,  593). 


CAESIUM  TRIHALIDES. 


19 


There  was  a  tendency  in  the  crystals  to  arrange  themselves  in 
parallel  position,  forming  plates  showing  large  a  faces,  but  the 


772 


m 


m 


separate  individuals  were  small,  scarcely  over  3  mm.  in  greatest 
diameter.  The  faces  gave  excellent  reflections.  The  crystals 
are  black,  transmit  a  brownish-red  light  only  on  the  thinnest 
edges,  and  are  too  opaque  for  optical  examination. 

CsBrIz.  —  On  two  separate  samples  of  this  salt  the  forms  a, 
£>,  c,  m,  d,  /,  and  e  were  observed.    The  crystals  are  thin  tables 
somewhat  lengthened  in  the  direction  of 
the  brachy-axis,  Fig.  4.     On  examining 
the  general  table,  it  will  be  seen  that  this 
is  the  only  one  of  the  first  five  salts  in 
which  the  angle  e  A  e  varites  considerably 
from  78°.     Here  the  variation  amounts 
to  a  little  over  one  degree,  but  in  all 
probability  this  is  not  to  be  accounted 
for  by  imperfections  in  the  crystals  or 
inaccuracy  in  the  observation,  for  from 
two  different  crops  of  crystals  good  reflections  and  almost 
identical  measurements  were   obtained.     The  crystals   were 
only  a  fraction  of  a  millimetre  in  thickness,  and  not  over  10 
mm.  long  in  the  direction  of  the  brachy-axis.    With  the  polar- 
izing microscope  the  tables  show  a  decided  pleochroism.     For 


20 


ON  A   SERIES  OF 


rays  vibrating  parallel  to  the  c  axis  the  color  is  dark  brown, 
almost  opaque,  while  for  vibrations  parallel  to  &  it  is  a  rich 
reddish  brown.  A  similar  though  less  marked  pleochroism 
was  observed  in  the  remaining  salts  of  the  series,  but  owing 
to  the  inability  to  obtain  orientated  pinacoid  sections,  it  could 
not  be  studied  satisfactorily.  In  convergent  polarized  light 
the  phenomena  were  not  very  distinct,  but  with  the  tables 
of  CsBrI2  apparently  an  obtuse  bisectrix  could  be  seen,  the 
optical  axis  being  in  the  macro-pinacoid  &. 


CsBr2I.  —  On  this  salt  the  forms  a,  <?,  m,  d,  /,  and  e  were 
observed.  The  habit  is  shown  in  Fig.  5.  The  crystals  were 
brilliant  and  gave  excellent  reflections.  Those  submitted  for 
measurement  were  about  3  mm.  in  greatest  diameter. 

Os  OlBrl.  —  On  this  salt  the  forms  £,  c,  m,  d,  /,  and  e  were 
observed.     The  habit  is  like  Fig.  5,  but  much  longer,  or  pris- 
matic, in  the  direction  of  the  brachy- 
axis.      The    crystals    were    about 
2  mm.  in  diameter  and  10  in  length. 
CsClzI.  —  This   compound  is  di- 
morphous. 

On  the  orthorhombic  modification 
the  forms  a,  <?,  TW,  c?,/,  and  e  were 
observed,  but  m  and  /  are  usually 
wanting.  The  habit  is  shown  in 
Fig.  6.  The  crystals  were  about 
2  mm.  in  diameter. 

The  hexagonal,  rhombohedral  variety  occurred  in  curious 
saddle-shaped  scales,  with  bright  crystal  faces  only  along 


CAESIUM  TRIIIALIDES.  21 

the  edges.  The  forms  which  were  observed  are  r  (1,  lOll), 
/  (-2,  0221),  and  a  (i-2,  1120),  Fig.  7.  Only  that  portion  is 
perfect  which  is  included  between  the  irregular  dotted  lines, 
the  upper  and  lower  angles  of  the  rhombohedrons  being 
truncated  by  irregular  warped  surfaces.  In  their  growth  the 
individuals  of  a  whole  series  of  crystals,  with  similar  orienta- 
tion, are  piled  upon  one  another  in  the  direction  of  the  vertical 
axis.  The  scales  are  about  6  mm.  in  diameter. 

The  measurement  which  was  taken  as  fundamental  is : 

r  A  r,  over  a,  10T1  A  01TT  =  99°  48' 

giving  for  the  length  of  the  vertical  axis,  c  =  0.96363.  The 
following  measurements  were  also  made : 

a  A  a  =  60°  0',  60°  1',  59°  59'        Calculated  60°  0' 
a  A/,  I2TOA022l  =    37°  45'  "         37°  49' 

The  remaining  compounds  containing  no  iodine  were  much 
more  unstable  than  those  previously  described.  By  making 
the  measurements  in  a  cold  room  very  satisfactory  results 
were  obtained,  the  crystals  retaining  enough  lustre  to  give 
good  reflections,  even  after  they  had  suffered  considerable 
decomposition. 

OsBr8.  —  The  forms  observed  on  this  salt  are  5,  m,  and  d. 
The  habit  is  short  prismatic,  with  either  m  or  d  predominating, 
while  b  is  usually  wanting.  Single  crystals  are  sometimes 
10  mm.  in  length,  but  groups  of  small  crystals  are  more  apt  to 
occur. 

Cs  ClBrz.  —  The  only  forms  observed  on  this  salt  are  m  and 
c.  The  habit  is  short  and  stout  prismatic.  Single  crystals  are 
sometimes  15  mm.  in  length. 

CsChBr.  — The  forms  observed  on  this  salt  are  <?,  TTZ,  and  d. 
It  crystallized  in  stout  prisms,  over  10  mm.  long,  terminated 
like  Fig.  1. 

Method  of  Analysis. 

The  samples  were  prepared  for  analysis  by  pressing  on 
paper.  The  drying  was  not  always  very  good,  both  on 


22  ON  A   SERIES   OF 

account  of  the  haste  sometimes  necessary  to  avoid  too  much 
decomposition,  and  on  account  of  the  great  tendency  of  the 
crystals  to  contain  cavities  filled  with  liquid. 

Caesium  was  invariably  determined  by  weighing  the  nor- 
mal halide  produced  by  heating.  In  some  cases  where  the 
resulting  normal  halide  was  slightly  contaminated  by  a 
higher  halogen,  this  was  replaced  by  the  proper  one  before 
weighing. 

Where  two  halogens  were  present,  they  were  determined  in 
the  usual  way  by  weighing  their  silver  salts  and  determining 
the  loss  in  weight  of  these  when  heated  in  chlorine.  In  the 
cases  where  all  three  halogens  were  present,  use  was  made  of 
the  extremely  satisfactory  method  described  by  Gooch  and 
Ensign.* 

Csls. 

This  can  be  made  by  dissolving  about  one-fourth  the  theo- 
retical amount  of  iodine  in  a  solution  of  one  part  of  cassium 
iodide  in  ten  parts  of  water.  It  generally  gives  a  crop  of 
brilliant,  slender  crystals.  If  a  larger  proportion  of  iodine  is 
used,  the  substance  generally  separates  in  the  form  of  crystal- 
line plates  without  distinct  faces.  They  are  possibly  a  dimor- 
phous form  of  the  substance.  If  weak  alcohol  is  used  as  a 
solvent  instead  of  water,  the  theoretical  amount  of  iodine  can 
be  taken  and  a  well-crystallized  product  is  obtained. 

The  following  numbers  show  the  composition : 

Found.  Calculated  for 

Slender  Crystals.          Plates.  CsI3. 

Csesium     25.41  23.71  25.88 

Iodine     72.67  .  .  .  74.12 

When  iodine  is  being  dissolved  in  a  warm  aqueous  solution 
of  Csl,  or  when  an  attempt  is  made  to  dissolve  Csls  in  warm 
water,  a  heavy  black  liquid  is  formed  at  about  73°  which 
solidifies  on  cooling  to  a  crystalline  mass.  It  is  much  richer 
in  iodine  than  CsI8  and  probably  contains  a  higher  polyiodide. 
Analyses  of  the  substance  gave  varying  results,  and  although 

*  Amer.  Jour.  Sci.,  III,  xl,  145,  1890. 


CAESIUM  TRIHALIDES.  23 

most  of  these  approached  the  composition  CsI6,  it  is  still  un- 
certain what  body  this  is.  The  low  melting-point  of  the 
substance  is  remarkable,  since  CsI3  melts  at  210°  and  iodine 
at  114°. 

To  find  the  solubility  of  CsI3  in  an  aqueous  solution  of  Csl, 
the  mother-liquor  from  a  crop  of  crystals  deposited  at  about 
20°  was  analyzed.  It  gave  : 

Csl          16.99  per  cent. 

I  (free)  0.416  per  cent  or  Csls  0.842  per  cent. 

The  specific  gravity  of  this  mother-liquor  was  1.154,  hence 
1  c.  c.  contained  0.0097gCsI3.  The  body  is  so  insoluble  that, 
were  we  to  use  Csl  in  the  place  of  KI  in  making  a  volumetric 
iodine  solution,  we  could  only  obtain,  at  ordinary  temperatures, 
a  solution  which  would  be  about  ^  normal. 

OsBrI2. 

Iodine  dissolves  in  considerable  quantity  in  a  hot  aqueous 
solution  of  caesium  bromide,  but  it  nearly  all  separates  on 
cooling.  It  is  therefore  necessary  to  use  a  mixture  of  alcohol 
and  water  in  preparing  this  trihalide.  A  good  crop  of  crystals 
was  obtained  by  dissolving  one-half  the  theoretical  iodine  in  a 
solution  of  one  part  of  caesium  bromide  dissolved  in  two  parts 
of  water  and  one  part  (by  volume)  of  alcohol. 

The  following  numbers  show  the  composition  of  the  crys- 
tals: 

•P       ,,  Calculated  for 

Found.  C8BrIj 

Caesium 28.54  28.48 

Bromine 18.11  17.13 

Iodine 52.01  54.39 

CsBrJ. 

This  may  be  made  by  dissolving  the  theoretical  amounts  of 
iodine  and  bromine  in  a  solution  of  one  part  of  caesium  bro- 
mide in  ten  parts  of  water.  A  considerable  excess  of  bromine 
does  not  interfere  with  its  formation. 

The  crystals  have  the  following  composition : 


24  ON  A    SERIES  OF 

w«,,r,^  Calculated  for 

Found.  CflBrjI 

Caesium       .....    31.32  31.67 

Bromine     .....     37.63  38.09 

Iodine    ......     29.57  30.24 

The  solubility  of  this  substance  in  water  was  approximately 
determined  by  estimating  the  free  halogens  volumetrically  in 
the  mother-liquor  from  a  recrystallization  at  about  20°.  The 
amount  found  corresponded  to  4.45  per  cent  of  CsBr2L 


Repeated  attempts  to  make  this  substance,  by  using  concen- 
trated solutions  of  caesium  chloride  and  iodine  in  mixtures  of 
water  and  alcohol  and  cooling  to  low  temperatures,  invariably 
failed. 

CsClBrl. 

This  may  be  made  by  dissolving  about  one-fourth  of  the 
theoretical  bromine  and  iodine  in  a  solution  of  one  part  of 
caesium  chloride  in  five  parts  of  water.  If  an  excess  of 
caesium  chloride  is  not  taken,  the  product  will  contain  too 
little  chlorine  and  too  much  bromine. 

An  analysis  of  the  product,  properly  prepared,  gave  : 

Vrm-nA  Calculated  for 

CsClBrl. 

Caesium       .     .    .    *    .  34.24  35.42 

Chlorine      .....  9.36  9.45 

Bromine      .....  19.96  21.30 

Iodine    ......  32.36  33.83 

If  a  large  excess  of  bromine  is  used,  an  impure  product 
results,  as  is  shown  by  the  following  analysis  of  a  sample  thus 
made: 

Found. 

Caesium     ........  36.11 

Chlorine    ........  9.36 

Bromine    ........  27.70 

Iodine  .........  24.83 

On  attempting  to  recrystallize  the  CsClBrl,  a  product  of  a 
darker  red  color  is  formed,  sometimes  accompanied  by  the 


CAESIUM   TRIHALIDES.  25 

separation  of  some  iodine.     The  following  analyses  were  made 
of  products  of  recrystallization  : 

"  A  "  was  from  a  single  recrystallization.  "  B  "  was  recrys- 
tallized three  times,  a  little  alcohol  being  added  the  last  time 
to  keep  iodine  in  solution.  "  C  "  was  recrystallized  five  times, 
each  time  with  the  addition  of  a  large  excess  of  bromine. 

Calculated  for      Calculated  for 
A.  B.  C.  CsClBrl. 


Caesium,  32.69  33.22  .  .  .  35.42  31.67 

Chlorine,  3.32  5.02  2.70  9.45  0. 

Bromine,  31.56  28.30  32.50  21.30  38.09 

Iodine,  30.91  31.78  30.99  33.83  30.24 

These  analyses  show  that  the  recrystallized  body  approaches 
CsBr2I,  but  that  a  part  of  the  chlorine  is  very  tenaciously  held. 
The  excess  of  bromine  used  in  the  case  "  C  "  had  apparently 
no  effect,  probably  because  caesium  and  iodine  were  present  in 
equivalent  quantities,  whereas,  in  the  case  previously  given,  in 
which  an  excess  of  bromine  was  used  in  presence  of  much 
caesium  chloride  in  preparing  the  body,  there  was  evidently  a 
contamination  with  CsClBr2. 

CsClJ. 

This  body  is  dimorphous,  the  form  apparently  depending 
upon  the  presence  or  absence  of  a  large  excess  of  caesium 
chloride  in  the  solution  from  which  it  crystallizes. 

The  rhombohedral  variety  is  usually  obtained  by  adding 
iodine  in  the  proportion  of  one  atom  to  one  molecule  of 
caesium  chloride  dissolved  in  about  ten  parts  of  water,  then 
passing  chlorine  into  the  liquid,  heated  nearly  to  boiling,  until 
the  iodine  just  dissolves,  and  finally  cooling.  If  an  excess  of 
chlorine  is  used,  the  body  CsCl4I  is  formed,  corresponding  to 
KC14I  discovered  by  Filhol.*  This  new  caesium  compound 
will  be  described  in  a  subsequent  article  in  connection  with 
several  other  new  bodies  of  the  same  class. 

The  orthorhombic  variety  of  CsCLJ  can  be  obtained  by  using 

*  Michalis,  Anorg  Chem.,  iii,  102 ;  Gmelin-Kraut,  II,  1,  82. 


26  ON  A   SERIES   OF 

three  or  four  times  as  much  caesium  chloride  as  in  the  other 
case,  the  other  conditions  remaining  unchanged. 

The  following  analyses  of  two  separate  products  of  each  of 
the  two  varieties  were  made : 


Rhombohedral. 
Found. 

Orthorhombic. 
Found. 

Calculated  for 
CsCl2I. 

Caesium, 
Chlorine, 
Iodine, 

39.20 
20.72 
37.81 

39.92 
21.08 
38.21 

3SA3 
19.78 
38.97 

40.00 
20.75 
38.88 

40.18 
21.45 
38.37 

On  recrystallizing  either  form  of  this  substance,  from  solu- 
tion in  hot  water,  the  rhombohedral  variety  is  usually  formed, 
owing  to  the  lack  of  an  excess  of  csesium  chloride.  It  is  not 
unusual,  however,  to  obtain  at  first,  as  the  solution  cools,  slen- 
der needles  evidently  of  the  orthorhombic  variety,  which 
afterward  become  surrounded  by  rhombohedral  crystals. 


To  make  this  substance,  one-half  the  calculated  amount  of 
bromine  is  added  to  a  solution  of  one  part  of  csesium  bromide 
in  three  parts  of  water,  the  whole  is  heated  with  vigorous 
shaking  until  the  liquid  bromine  disappears,  and  then  slowly 
cooled.  Crystals  gave  on  analysis  : 

Calculated  for 
Found.  CsBr3. 

Caesium  ......    35.12  35.66 

Bromine      .....     61.53  64.34 

In  preparing  this  body  there  usually  remains,  when  the 
liquid  bromine  disappears  on  heating  the  solution,  a  heavy  red- 
dish liquid  much  lighter  in  color  than  bromine.  It  is  without 
doubt  a  higher  polybromide,  and  it  probably  corresponds  to 
the  easily  fusible  substance  already  mentioned  as  a  probable 
higher  polyiodide.  An  investigation  of  its  composition  will 
soon  be  made. 

CsClBrz. 

The  formation  of  this  body  was  mentioned  at  the  beginning 
of  this  article  in  connection  with  the  discovery  of  the  new 


CESIUM  TRIHALIDES.  27 

series  of  salts.  It  can  be  made  by  adding  about  one-half  the 
theoretical  bromine  to  a  solution  of  caesium  chloride  in  about 
five  parts  of  water,  dissolving  by  heat  and  cooling. 

The  analyses  of  two  products  are  given  below.  The  "  pre- 
cipitate "  resulted  from  adding  bromine  to  a  cold  csesium 
chloride  solution,  and,  being  finely  divided  as  well  as  the  most 
unstable  compound  of  the  series,  it  suffered  a  considerable 
amount  of  decomposition,  although  time  was  not  taken  to  dry- 
it  thoroughly. 

Found<  Calculated  for 


Precipitate. 

Crystals. 

CsClBr2, 

Caesium, 

40.62 

42.14 

40.49 

Chlorine, 

12.64 

13.24 

10.81 

Bromine, 

39.61 

42.93 

48.70 

Water, 

6.45 

1.72 

0. 

CsCl.Br. 

This  substance  may  be  made  by  adding  the  calculated 
amount  of  bromine  to  a  solution  of  csesium  chloride  in  five 
parts  of  water,  warming  enough  to  keep  CsClBr2  in  solution, 
and  passing  chlorine  in  excess. 


Analysis  gave 

Caesium  ......    46.25  46.83 

Chlorine     .....    24.15  25.00 

Bromine      .....     26.05  28.17 

Os  C18. 

Efforts  to  prepare  this  substance  by  passing  chlorine  into 
saturated  aqueous  solutions  of  csesium  chloride,  cooled  by  a 
freezing-mixture,  did  not  succeed.  It  was  noticeable  that  the 
compound  C1.5H2O  was  not  formed  under  these  circumstances. 

Other  Trihalides. 

Johnson's  KI8*  is  undoubtedly  analogous  to  the  csesium 
compounds.  An  investigation  of  this  and  other  potassium 

*  J.  Chem.  Soc.,  1877,  i,  249. 


28  02V  A    SERIES   OF 

trihalides,  as  well  as  the  corresponding  rubidium  compounds, 
is  now  in  progress  in  this  laboratory,  and  an  effort  will  be  made 
to  prepare  similar  compounds  with  still  other  metals. 

The  compound  KI2(CN)*  and  the  body  NH4I8,  which  John- 
son describes  f  as  very  similar  to  KI8,  should  be  mentioned  in 
this  connection. 

There  have  been  described  a  great  number  of  trihalides  of 
both  natural  and  artificial  organic  bases.  These  are  mostly 
triiodides,  but  there  are  among  them  a  number  of  tribromides 
and  also  mixed  trihalides,  especially  of  the  type  RC12I.  These 
organic  bodies^  are  evidently  analogous  to  the  caesium  com- 
pounds under  consideration,  but  since  they  have  not  been 
sufficiently  studied  to  throw  any  light  on  the  structure  or  crys- 
talline form  of  trihalides  in  general,  they  will  not  be  mentioned 
in  detail  here. 

Theoretical  Considerations. 

Thus  far  in  this  article,  the  simplest  possible  formula?  have 
been  used.  The  probable  structure  of  the  compounds  will 
now  be  discussed. 

The  trihalides  previously  known  have  been  usually  con- 
sidered as  weakly  combined  addition-products.  Mendele*eff,§ 
for  example,  says  that  the  instability  with  which  I2  unites  with 
KI  and  N(CH8)4I  is  analogous  to  the  instability  of  many 
cryohyd rates,  e.  g.,  HC1.2H2O.  It  must  be  noticed  that 
some  of  the  csesium  trihalides  are  very  stable,  but  this  fact  is 
evidently  due  to  the  strong  positive  character  of  the  metal,  and 
since  others  among  them  are  comparatively  unstable,  it  can 
have  no  important  bearing  on  their  structure. 

Johnson  ||  advances  the  formula  K2T6  for  potassium  triiodide 

*  Langlois,  Ann.  Chim.  Phys.,  [Ill]  Ix,  220.        t  J.  Chem.  Soc.,  1878,  397. 

J  See  the  following  articles:  Weltzien,  Ann.  Ch.  Ph.,  xci,  33;  xcix,  1. 
Miiller,  ibid.,  cviii,  5.  Hubner,  ibid.,  ccx,  368.  Ladenburg,  ibid.,  ccxvii,  122. 
Zincke  and  Lawson,  ibid.,  ccxl,  123.  Zincke  and  Artzberger,  ibid.,  ccxlix,  366. 
Jb'rgensen,  J.  pr.  Ch.,  II,  vols.  ii,  iii,  xiv,  and  xv.  Dafert,  Monatshefte,  iv,  496. 
Dittmar,  Berichte,  xviii,  1612.  Ostermayer,  ibid.,  xviii,  2298.  Kamensky, 
ibid.,  xi,  1600.  Tilden,  J.  Chem.  Soc.,  xviii,  99.  Hoogewerff  and  Dorp,  Rec. 
Trav.  Chim.,  iii,  361. 

§  Grundlagen  der  Chemie,  p.  563,  foot-note  63. 

||  J.  Chem.  Soc.,  1878,  183. 


CAESIUM  TRIHALIDES.  29 

with  no  better  reason  than  the  existence  of  a  higher  iodide  of 
mercury,  HgI6.*  This  formula  may  be  dismissed  at  once,  for 
there  is  no  more  ground  for  it  than  for  writing  K2I2  because 
HgI2  exists,  and  moreover,  if  the  caesium  salts  were  Cs2X6,  we 
should  expect  to  find  in  the  series  such  compounds  as  Cs2Cl6I, 
Cs2Cl8l8,  etc.,  none  of  which  were  discovered. 

Since  the  members  of  the  caesium  series  are  crystallographi- 
cally  isomorphous,  they  must  all  have  the  same  structure,  and, 
as  has  just  been  shown,  no  multiple  of  the  formula  CsX8  is 
probable. 

A  possible  explanation  of  the  caesium  trihalides  may  be 
made  by  supposing  the  metal  to  act  trivalently,  and  the  fol- 
lowing arguments  seem  to  favor  this  view : 

1st.  Caesium  has  the  highest  atomic  weight  of  the  alkali- 
metals,  and  it  is  a  noticeable  fact  that,  among  the  elements 
in  general,  those  with  higher  atomic-weights  in  a  group  have 
the  greater  tendency  to  act  with  variable  quantivalence.  2d. 
Caesium  is  univalent  in  its  ordinary  compounds,  and,  following 
the  general  rule,  the  next  higher  quantivalence  should  be 
three.  3d.  Caesium  is  in  the  same  group  as  gold  in  Men- 
dele'eff's  periodic  system  of  the  elements,  and  it  is  well  known 
that  this  element  acts  univalently  and  trivalently. 

On  the  other  hand,  the  following  arguments  are  in  favor  of 
considering  the  bodies  double  salts :  1st.  The  compounds  IBr, 
IC1,  and  BrCl  are  definite  bodies ;  and  all  the  trihalides  may  be 
considered  as  molecular  compounds  of  these,  and  also  the 
molecules  L  and  Br2,  with  normal  halides.  2d.  The  fact  that 
CsBr2I  is  more  stable  than  CsBrI2,  and  that  CsCl2Br  is  more  so 
than  CsClBr^  showing  that  the  stability  of  these  bodies  does 
not  entirely  depend  upon  the  volatility  of  the  halogens  con- 
tained in  them,  indicates  that  the  halogen  atoms  have  much 
influence  on  each  other,  and  that  at  least  two  of  them  are 
probably  bound  together.  A  consideration  of  the  fact  that 
CsCl2I  is  a  very  stable  body,  while  CsClLz  probably  cannot  be 
prepared,  leads  to  the  same  conclusion.  3d.  It  has  been  pointed 
out  by  Godeffroy  f  that  the  simple  salts  of  caesium  are  as  a  rule 
*  Jorgensen,  J.  pr.  Ch.,  II,  ii,  357.  t  Berichte,  ix,  1365. 


30  ON  A    SERIES  OF 

more  soluble  than  the  corresponding  rubidium  and  potassium 
salts,  while  with  the  double  salts  the  reverse  is  true.  Work 
now  in  progress  in  this  laboratory  shows  that  the  rubidium  and 
potassium  trihalides,  as  far  as  they  have  been  investigated, 
increase  in  solubility  towards  potassium ;  hence,  if  the  rule 
holds  true,  they  must  be  double  salts.  4th.  The  new  salt 
CsI.AgI,*  an  undoubted  double  salt,  shows  a  close  relation  to 
the  trihalides  in  its  system  of  crystallization,  in  the  ratio  of 
the  two  axes  which  alone  were  determined,  and  in  its  cleav- 
age.f  The  salt  KI.AgI J  has  been  prepared,  but  it  has  not  yet 
been  procured  in  crystals  fit  for  measurement.  Work  will  be 
continued  on  this  class  of  compounds. 

The  evidence  which  has  just  been  given  points  strongly 
towards  considering  the  trihalides  as  double  salts.  The  con- 
siderations based  on  the  axial  relations  of  the  crystals,  which 
have  been  given  in  the  crystallographic  part  of  this  article, 
also  indicate  that  these  bodies  cannot  be  viewed  as  compounds 
of  trivalent  caesium,  and,  moreover,  that  a  single  halogen 
atom  of  highest  atomic  weight  plays  an  important  part  in  their 
structure.  One  view  of  the  possible  position  of  this  peculiar 
atom  may  be  that  it  is  a  trivalent  atom  united  to  the  others  in 

the  manner  indicated  by  the  general  formulae  Cs  —  I<v  and 

*  This  was  made  by  dissolving  Agl  in  a  concentrated,  hot  solution  of  Csl 
and  cooling.  It  forms  tufts  of  hair-like  crystals,  very  seldom  large  enough  to 
measure. 

Analysis  gave  C^SS^U 

Silver 19.03  21.82 

Iodine 50.91  51.32 

Caesium 26.86 

t  CsI.AgI  crystallizes  in  the  orthorhombic  system.  It  was  obtained  in  long 
needles,  not  over  £  mm.  in  diameter  and  too  small  to  show  distinct  end  faces. 
A  pinacoid  and  two  other  forms  occur  in  the  prismatic  zone  which  correspond 
to  c(001),  #(012),  and  c?(011)  of  the  trihalide  series.  Of  these  c  and  g  are  the 
best  developed,  while  d  is  very  small.  Five  independent  measurements  of 
c  A  g  gave  values  varying  between  27°  29'  and  27°  44',  the  average  being  27°  36', 
which  gives  the  ratio  b  :  c  =  1  :  1.0456.  The  crystals  show  an  imperfect  cleav- 
age parallel  to  a  (100)  and  probably  a  second  parallel  to  c,  but  they  were  too 
small  to  allow  of  this  being  determined  with  certainty.  Under  the  polarizing 
microscope  they  show  parallel  extinction. 

\  Boullay,  Ann.  Chim.  Phys.,  II,  xxxiv,  377. 


CAESIUM  TRIHALIDES. 


31 


Cs  — Br<-^.      This  view  may  be   objected  to   because   the 
strongest  halogen  atom  is  not  directly  united  to  the  caesium. 

V 

The  structure  Cs  —  X<  n  is  scarcely  admissible  in  the  com- 

X 

pound  CsI.AgI  on  account  of  the  probable  invariable  univa- 
lence  of  silver. 

Another  view  of  the  position  of  the  peculiar  iodine  or 
bromine  atom  may  be  based  upon  the  idea,  so  ably  advocated 
by  Remsen,*  that  a  bivalent  group  of  two  halogen  atoms  acts 
the  same  part  in  double  halides  that  oxygen  takes  in  ordinary 
oxygen  salts.  Supposing  that  a  halogen  atom  of  highest  atomic 
weight  is  linked  to  the  caesium  atom  by  means  of  the  other 
two  halogen  atoms,  acting  as  a  bivalent  group,  the  trihalides 
have  the  following  formulae  :  — 


Cs— (II)— I 
Cs— (BrI)— I 
Cs— (BrBr)—  I 
Cs— (ClBr)— I 
Cs— (C1C1)— I 
[Cs-(ClI)— I] 


Cs—  (BrBr)—  Br 
Cs— (ClBr)— Br 
Cs— (C1C1)— Br 


[Cs— (C1C1)— Cl] 


These  formulae  allow  the  supposition  that  the  most  negative 
halogen  atom  is  in  direct  union  with  the  caesium.  They  are 
consistent  with  the  view  that  there  are  two  symmetrical  series 
of  compounds,  one  with  an  iodine  atom,  the  other  with  a 
bromine  atom  in  a  special  position.  On  these  grounds  they 
seem  quite  plausible. 

Assuming  that  the  structure  of  the  trihalides  is  represented 
by  the  above  formulae,  a  comparison  of  their  relative  stability 
leads  to  the  view  that  the  linking  group  of  two  halogen  atoms 
causes  greater  stability  when  composed  of  like  atoms  than 
when  these  atoms  differ.  The  groups  (II)  (BrBr)  and  (C1C1) 
occur  in  the  comparatively  stable  compounds,  while  (ClBr)  is 
in  the  most  unstable  body  of  the  "  bromine  series,"  (BrI)  is  in 


*  On  the  Nature  and  Structure  of  Double  Halides,  Amer.  Chem.  Jour., 
xi,  291. 


32  ON  A   SERIES   OF  CAESIUM  TRIHALIDES. 

the  least  stable  one  of  the  "  iodine  series,"  and  the  compound 
which  should  contain  (C1I),  with  the  least  closely  related  halo- 
gens, could  not  be  prepared.  There  is  a  possible  exception  in 
the  body  Cs — (ClBr) — I,  for  it  has  not  been  noticed  that  the 
stability  of  this  varies  to  any  marked  extent  from  Cs — (C1C1) 
— I.  The  same  view  of  the  effect  of  the  identity  of  the  link- 
ing halogen  atoms  will  probably  apply  to  all  double  halides, 
for  it  is  certain  that  very  few  of  these  containing  different 
halogens  are  known,  although  this  may  be  partly  due  to  the 
fact  that  mixed  double  halides  have  not  been  sufficiently 
studied.  An  investigation  of  the  double  halides  of  caesium 
and  mercury,  now  in  progress,  indicates  that  the  generalization 
will  apply  in  this  case.  Whatever  may  be  the  true  structure 
of  double  halides,  this  influence  of  the  identity  of  the  halogens 
in  the  combining  simple  salts  probably  depends  upon  the  same 
broad  chemical  law  which  causes,  for  example,  two  oxides  or 
two  sulphides  to  combine  more  readily  than  an  oxide  and  a 
sulphide  of  the  same  elements,  and  which  causes  sulphates  to 
combine  with  other  sulphates  more  readily  than  they  combine 
with  nitrates  and  other  dissimilar  salts. 

The  present  communication  may  be  considered  as  prelimi- 
nary to  a  wider  study  of  polyhalides  and  double  halogen  salts. 
It  is  hoped  that  other  series,  studied  chemically  and  crystallo- 
graphically,  may  give  valuable  results. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
December,  1891. 


ON  THE  RUBIDIUM  AND  POTASSIUM 
TRIHALIDES.* 

BY  H.  L.   WELLS   AND  H.  L.  WHEELER. 

WITH  THEIR  CRYSTALLOGRAPHY. 

BY  S.   L.  PENFIELD. 

THE  discovery  of  a  series  of  csesium  trihalides  f  has  led  the 
writers  to  investigate  the  analogous  rubidium  and  potassium 
compounds.  The  following  table  gives  a  list  of  the  bodies 
which  we  have  been  able  to  prepare,  together  with  the  csesium 
series  for  comparison.  The  compound  KI.I2  had  been  pre- 
viously prepared  by  Johnson.J 

CsI.I2  RbI.I2  KLI2 

CsBr.I2  

CsBr.BrI  RbBr.BrI  KBr.BrI 

CsCLBrI  RbCLBrl  

csci.cn  Rbci.cn  KCI.CII 

CsBr.Br2  RbBr.Br2  

CsCl.Br2  RbCl.Br2  

CsCl.ClBr  RbCl.ClBr  

It  is  to  be  noticed  that  there  is  but  one  member  lacking  in 
the  rubidium  series  to  make  it  as  complete  as  that  of  caesium. 
We  have  repeatedly  tried  to  prepare  this  compound,  RbBr.I2, 
using  alcoholic  solutions  of  varying  strength  and  great  con- 
centration at  low  temperatures,  but  with  no  success.  The 
failure  to  make  this  body  doubtless  depends  upon  the  com- 
parative instability  of  the  rubidium  series.  We  have  even 
attempted  to  prepare  RbCl.I2  and  RbCl.Cl2,  corresponding 

*  Amer.  Jour.  Sci.,  xliv,  July,  1892. 
t  Ibid.,  Ill,  xliii,  17. 
J  J.  Chem.  Soc.,  1877,  241. 
3 


34  ON  THE  RUBIDIUM  AND 

to  which  no  caesium  compounds  could  be  made,  but,  as  was 
anticipated,  these  efforts  were  entirely  without  success. 

In  the  potassium  series,  only  those  bodies  could  be  prepared 
which  correspond  to  the  more  stable  caesium  and  rubidium 
compounds.  They  show  a  great  decrease  in  stability  in 
comparison  with  the  rubidium  compounds.  A  product  was 
obtained  at  a  very  low  temperature,  which  was  probably  KBr. 
Br2,  but  we  did  not  make  a  satisfactory  analysis  of  it. 

We  have  attempted  to  prepare  a  number  of  sodium  and 
lithium  trihalides.  There  is  no  doubt  that  some  of  them 
exist,  but  they  are  so  extremely  soluble  and  unstable  that  we 
have  abandoned  work  in  this  direction. 

Method  of  Preparation.  —  The  rubidium  and  potassium 
compounds  are  made,  like  the  caesium  series,  by  dissolving  a 
normal  halide  with  the  proper  halogen  or  halogens  in  water 
with  the  aid  of  heat  and  cooling  to  crystallization.  The 
members  of  the  rubidium  series,  being  very  soluble,  require 
very  concentrated  solutions  for  their  preparation.  The  potas- 
sium compounds,  being  still  more  soluble,  require  the  greatest 
possible  degree  of  concentration,  and  are  usually  best  obtained 
by  exposing  the  solutions  for  a  considerable  time  to  a  winter 
temperature,  evaporation  in  the  desiccator  being  sometimes 
also  necessary. 

Color.  —  The  colors  of  the  rubidium  and  potassium  com- 
pounds are  very  similar  to  those  of  the  corresponding  members 
of  the  caesium  series,  but,  since  they  usually  form  larger 
crystals,  their  apparent  color  is  generally  somewhat  darker. 
They  vary  in  color  from  brilliant  black  in  RbI.I2  and  KI.I2, 
through  various  shades  of  yellowish-red  and  orange  to  bright 
yellow  in  the  compound  RbCl.ClBr.  In  all  the  compounds 
that  have  been  prepared,  the  color  becomes  lighter  as  the  sum 
of  the  atomic  weights  of  the  three  halogen  atoms  decreases. 

Stability.  —  It  has  been  found  by  experiment  that  the 
potassium  trihalides  are  much  less  stable  on  exposure  to  the 
air  than  the  corresponding  rubidium  compounds,  while  these 
in  turn  are  less  stable  than  the  members  of  the  caesium  series. 
The  same  relative  stability  of  the  three  series  is  shown  by  the 


POTASSIUM  TRIHALIDES.  35 

temperatures  at  which  they  are  completely  decomposed   by 
rapid  heating  as  given  below : 

Approximate  Temperature  of  Whitening. 


CsI.I2,  330° 
CsBr.Brl,  320° 
CsCLClI,  290° 
CsCLBrl,  290° 

KbI.I2,  270° 
EbBr.BrI,  265° 
BbCLClI,  265° 
BbCLBrl,  200° 

KI.I2,  225° 
KBr.BrI,  180° 
KC1.C1I,  215° 

CsBr.Br2,  160° 

KbBr.Br2,  140° 

CsCl.ClBr,  150° 

BbCLClBr,  110° 

CsCLBr.,  150° 

BbCUBr,,  80° 

Fusibility.  —  The  melting-points  of  the  analogous  com- 
pounds become  lower  from  caesium  to  potassium.  In  the 
open  capillary  tube  RbI.I2  melts  at  194°  and  RbCl.ClI  at 
208°,  while  all  the  other  rubidium  compounds  whiten  without 
melting.  The  potassium  compounds  give  practically  the 
same  melting-points  in  open  as  in  sealed  tubes.  The  follow- 
ing table  gives  the  approximate  melting-points  in  sealed 
tubes  : 

CsLI,,  201°-208°  KbIJ2,  190°  KI.I2, 38°* 

CsBr.Brl,  243°-248°  KbBr.BrI,  225°  KBr.BrI,  60° 

CsCl.ClI,  225° -230°  BbCl.CH,  180° -200°  KC1.C1I,  60° 

CsCLBrl,  225°-235  BbCLBrl,  205°  

CsBr.Br2,  180°  EbBr.Br2,  whitens  

CsCl.ClBr,  205°  BbCLClBr,  whitens  

CsCl.Br2,  191°  KbCl.Br2,  76°?  

Behavior  with  Solvents.  —  The  extreme  solubility  of  the 
rubidium  and  potassium  trihalides  in  water  has  already  been 
referred  to,  and  it  has  been  pointed  out  that  the  members  of 
the  potassium  series  are  the  most  soluble.  The  rubidium 
compounds  which  contain  iodine  can  be  recrystallized  from 
water  without  difficulty.  These  four  bodies  containing  rubid- 
ium and  iodine  are  sufficiently  stable  to  be  soluble  in  alcohol, 
while  the  remaining  rubidium  compounds,  as  well  as  all  the 

*  Johnson  gives  45°  for  the  melting-point  of  this  compound  (1.  c.). 


36  ON  THE  RUBIDIUM  AND 

potassium  compounds,  are  more  or  less  readily  decomposed 
by  alcohol  with  the  separation  of  normal  halides.  Ether 
decomposes  all  the  rubidium  and  potassium  compounds,  leav- 
ing normal  halides  undissolved. 

Crystallography. 

The  rubidium  trihalides  crystallize  in  the  orthorhombic 
system  and  are  isomorphous  with  the  corresponding  csesium 
compounds,  showing  a  close  similarity  both  in  crystalline 
habit  and  in  axial  ratios. 

The  forms  which  have  been  observed  are : 

a,  100,  i-1  d,  Oil,  1-r 

b,  010,  i-i  f,  021,  2-r 

c,  001,    0  e,  102,  \-l 
m,  110,   1  p,  111,  1. 

With  the  exception  of  the  pyramid  p,  which  was  observed 
as  a  small  face  only  on  RbI.I2,  these  are  the  same  as  were 
observed  on  the  csesium  trihalides,  while  the  brachydome  g, 
012,  J-i,  which  was  found  only  on  CsI.I2,  was  not  observed  on 
any  of  the  rubidium  compounds. 

Of  the  three  potassium  trihalides  which  were  examined, 
only  one,  KBr.BrI,  was  orthorhombic  like  the  caesium  and 
rubidium  compounds.  The  others,  KI.I2  and  KC1.C1I,  are 
monoclinic,  but  they  can  be  referred  to  axes  which  are  similar 
to  those  of  the  orthorhombic  series. 

The  cleavage  of  the  rubidium  trihalides  is  perfect  parallel  to 
c,  less  perfect  parallel  to  a ;  neither  is  easily  produced.  The 
crystals  are  very  brittle  and  usually  break  with  a  conchoidal 
fracture.  The  potassium  trihalides  are  exceedingly  brittle, 
and  no  cleavage  was  observed.  The  optical  properties  were 
not  studied,  owing  to  the  difficulty  of  preparing  orientated 
sections. 

In  the  following  table  the  axial  ratios  of  all  the  alkali- 
metal  trihalides  are  given,  arranged  as  in  the  csesium  paper. 
In  the  table  of  angles  those  which  were  chosen  as  fundamen- 
tal are  marked  by  an  asterisk. 


POTASSIUM  TRIHALIDES. 


37 


ii. 


a  :  b  :  c 

a  :  b  :  c 

Series  with  iodine. 

(CsI.I2 
J  EbU, 

0.6824  :  1  :  1.1051 
0.6858  :  1  :  1.1234 

1 
1 

1.4655 
1.4582 

1.6196 
1.6381 

(KLI, 

(  0.7065  :  1  :    ... 

1 

1.4154 

|  Monoclinic,  a  =  86°  47£' 

a  =  86 

0  47$' 

CsBr.I2 

0.6916  :  1  :  1.1419 

1 

1.4460 

1.6511 

f  CsBr.BrI 

0.7203  :  1  :  1.1667 

1 

1.3882 

1.6196 

}  EbBr.Brl 

0.7130  :  1  :  1.1640 

1 

1.4025 

1.6325 

(  KBr.BrI 

0.7158  :  1  :  1.1691 

1 

1.3970 

1.6333 

(  CsCLBrl 

0.7230  :  1  :  1.1760 

1 

1.3831 

1.6268 

t  EbCLBrl 

0.7271  :  1  :  1.1745 

1 

1.3753 

1.6153 

(  CsCl.ClI 
J  EbCl.ClI 

0.7373  :  1  :  1.1920 
0.7341  :  1  :  1.1963 

1 

1 

1.3563 
1.3622 

1.6167 
1.6296 

(Kci.cn 

(  0.7335  :  1  :  1.2204 

1 

1.3633 

1.6638 

1  Monoclinic,  a  =  83°  20'         a  =  83°  20' 

Series  without  iodine. 

(  CsBr.Br2 

0.6873  :  1    1.0581 

1:1.4550    1.5395 

(  EbBr.Br2 

0.6952  :  1    1.1139 

1:1.4384    1.6023 

(CsCLBr. 

0.699    :  1      ... 

1  :  1.430 

(EbCl.Br2 

0.70      :  1    1.1269 

1  :  1.43        1.61 

JCsCLClBr 

0.7186:1    1.1237 

1:1.3917    1.5638 

i  EbCl.ClBr 

0.7146:1    1.1430 

1  :  1.3994    1.5995 

m  A  m,  110  A  fiO          d  A  d,  Oil 

A  Oil           e  A  c,  102  A  102 

EbI.I2 

*68°  53'              *96° 

39'              78°  38' 

KI.I2 

*70°  34' 

EbBr.Brl 

70°  58'              *98° 

40'            *78°  27' 

KBr.BrI 

71°  12'              *98° 

55'              78°  28' 

EbCLBrl 

72°    2'              *99° 

10£'          *77°  51' 

EbCl.ClI 

72°  34'            *100° 

13'            *78°  21' 

KCi.cn 

72°  54' 

*79°    8' 

EbBr.Br2 

*69°  37'              *96° 

10'              77°  24' 

EbCLBr2 

*70  approx.         *96° 

58'              76°  appro 

EbCl.ClBr 

71°    6f              *97° 

38'            *77°  18' 

A  comparison  of  the  axial  ratios  of  the  trihalides  shows 
that  the  replacement  of  csesium  by  rubidium,  and  in  one  case 


38  ON   THE  RUBIDIUM  AND 

by  potassium,  has  little  or  no  effect  on  the  form,  while  in  two 
of  the  compounds  potassium  causes  a  change  in  symmetry 
without  much  change  in  the  axes.  It  is  evident  that  the 
rubidium  salts,  like  those  of  caesium,  may  be  arranged  in  two 
symmetrical  series,  one  with  and  the  other  without  iodine,  in 
which  the  ratio  of  two  axes  remains  nearly  constant  through- 
out, while  the  third  varies,  and  the  conclusions  which  were 
arrived  at  in  our  previous  paper  concerning  the  constitu- 
tion of  the  caesium  trihalides  are  confirmed  by  the  rubidium 
compounds. 

The  rubidium  trihalides  have  a  strong  tendency  to  crystal- 
lize, and  the  solubility  is  such  that,  from  solutions  of  not  over 
50  c.  c.  in  volume,  large  and  magnificent  crystals  several  cen- 
timetres in  length,  can  readily  be  obtained.  The  size  of  the 
crystals  seems  often  dependent  only  upon  the  volume  of  the 
solution  and  the  size  of  the  vessel  containing  it.  Many  of 
the  large  crystals  are  complex,  being  built  up  of  smaller  ones 
in  parallel  position.  Some  of  the  crystallizations  were  as 
beautiful  as  any  that  we  have  ever  seen. 

The  rubidium  trihalides  containing  iodine  were  measured 
at  ordinary  temperatures ;  those  without  iodine  and  the  potas- 
sium trihalides  at  about  0°  C.  It  was  found  that  the  stability 
of  the  compounds  increased  very  rapidly  with  a  diminution 
in  temperature  and,  by  working  in  the  cold,  no  difficulty  was 
experienced  in  making  accurate  measurements  of  the  more 
unstable  salts.  It  is  not  considered  necessary  to  give  with 
each  trihalide  a  table  of  measured  and  calculated  angles,  but 
in  all  cases  where  a  series  of  accurate  measurements  were 
obtained,  they  agreed  closely  with  the  calculated. 

EbI.I2.  —  The  forms  6,  c,  m,  d,  f,  e,  and  p  were  observed. 
Of  these/  and  p  were  always  small  and  frequently  wanting. 
The  habit  is  shown  in  Fig.  1. 

RbBr.BrL  —  The  forms  of  a,  c,  m,  d,  and  e  were  observed. 
The  habit  is  shown  in  Fig.  2. 

KbOl.Brl. — The  forms  a,  d,  and  e  were  observed.  The 
pinacoid  a  is  usually  wanting,  and  the  simple  habit  shown  in 
Fig.  3  prevails. 


1. 


POTASSIUM  TRIHALIDES. 
2. 


39 


ThQ  forms  a,  d,  and  e  were  observed.  The 
habit  is  shown  in  Fig.  4. 

RbBr.Br*.  —  The  forms  a,  b,  m,  d,  and  /  were  observed. 
The  habit  is  shown  in  Fig.  5. 

RbCl.Br*. —  The  forms  5,  c,  m,  c?,  and  e  were  observed. 
The  habit  is  shown  in  Fig.  6.  The  tendency  of  this  salt  is 
to  crystallize  in  small  scales ;  it  is  also  the  most  unstable  of 
the  rubidium  series,  so  that  we  considered  it  fortunate  that 


we  were  able  to  make  out  the  axial  ratio.  The  only  faces 
which  yielded  good  reflections  were  b  and  c?,  which  established 
accurately  the  relation  between  the  b  and  c  axes,  while  only 
approximate  measurements  were  obtained  from  the  other  faces. 

RbCl.ClBr. —  The  forms  a,  5,  m,  d,  and  e  were  observed. 
The  habit  is  like  Fig.  2,  except  that  c  is  wanting. 

KHz.  —  This  occurs  in  very  simple  monoclinic  crystals. 
If  the  solution  is  cooled  slowly  it  forms  in  stout  prisms,  but 
by  rapid  cooling  a  network  of  fine  needles  is  obtained.  In 
order  to  make  this  salt  and  the  monoclinic  KC1.C1I  conform 
to  the  position  which  has  been  adopted  for  the  orthorhombic 
trihalides,  it  is  necessary  to  deviate  from  the  ordinary  custom 


40 


ON  THE  RUBIDIUM  AND 


and  make  the  clino-axis  slope  from  right  to  left  instead  of 
from  back  to  front.  The  faces  are  taken  as  6,  010,  i-l ;  <?,  001, 
0  and  ?tt,  110,  /.  The  crystals  are  not  sufficiently  modified 
to  determine  more  than  two  axes,  but  taking  as  fundamental 
measurements,  b  A  7/1,  010  A  110  =  54°  43'  and  c  A  c  (re-entrant 
angle  of  twin  crystal)  =  6°  25',  the  following  axial  ratio  is 
obtained,  a  :  b  =  .7065  :  1 ;  a  =  010  A  001  =  86°  47  J'.  The 
angle  m  A  c,  110  A  001,  was  measured  91°  55'  and  91°  50',  cal- 
culated 91°  51'.  Fig.  7  represents  a  twin  crystal  in  the  above 
position.  Fig.  8  represents  a  simple  crystal  in  the  ordinary 
monoclinic  position,  with  d  as  the  clino  axis.  The  axial  ratio 
for  this  position  is,  d:t  =  1.4154  :  1 ;  0  =  86°  47  J'. 


m 


"s/ 


KBr.BrL  —  The  forms  «,  5,  w,  c?,  /,  and  e  were  observed. 
The  habit  is  shown  in  Fig.  9.  This  salt  differs  from  all  of 
the  other  alkali-metal  trihalides  in  having  the  brachy  prism 
w,  120,  i-2,  instead  of  the  unit  prism  m.  The  fundamental 
measurements  were  a  A  n  100  A  120  =  55°  4'  and  d  A  d,  Oil 
A  Oil,  =  98°  55'. 

KCL  OIL  —  This  crystallizes  in  long  needles  belonging  to 

the  monoclinic  system,  Fig.  10. 
Taking  b  as  the  clino  axis,  the 
forms  are  a,  100,  i-i;  6,  010,  i-l; 
e,  001,  0  ;  x,  032,  f-i,  and  «,  102,  \-i. 
The  measurements  taken  as  funda- 
mental are  c  A  5, 001  A  010  =  96°  40', 
e  A  e,  102  A  102  =  79°  8',  and  c  A  z,  001  A  032  =  66°  35',  from 


to. 


POTASSIUM  TRIHALIDES.  41 

which  the  following  axial  ratio  was  calculated,  a  :  b  :  c  —  .7335 
:  1  :  1.2204,  a  =  83°  20'.  If  taken  in  the  ordinary  monoclinic 
position  with  e  as  the  prism  110  and, a:  as  the  orthodome 
101,  the  axial  ratio  from  the  above  measurements  becomes 
d:~b:c  =  .8319  :  1  :  .4544;  0  =  83°  20'. 

Method  of  Analysis. 

The  methods  used  for  the  analyses  of  the  potassium  and 
rubidium  trihalides  were  exactly  the  same  as  those  men- 
tioned in  the  article  on  caesium  trihalides. 

The  crystals  were  prepared  for  analysis  by  pressing  between 
papers  and  at  the  same  time  crushing  them  somewhat.  In 
some  cases,  where  the  bodies  were  very  easily  decomposed, 
this  was  done  in  cold  weather  out  of  doors,  but,  even  with  this 
precaution,  it  was  not  possible  to  dry  them  very  thoroughly  or 
to  avoid  a  considerable  amount  of  decomposition. 

RU.I*. 

This  body  can  be  prepared  by  dissolving  55  g.  of  rubidium 
iodide  in  enough  water  to  make  a  solution  of  50  c.  c.,  adding 
60  g.  of  iodine,  warming  until  solution  takes  place,  and  cooling 
to  ordinary  temperature.  A  mass  of  large  crystals  in  parallel 
position,  forming  steps,  is  usually  formed. 

Analysis  gave  <%$$* 

Kubidium  ....     18.32  18.32  18.33 

Iodine 81.07  .  .  .  81.67 

A  specific  gravity  determination,  made  in  the  mother-liquor 
at  22°,  gave  the  number  4.03.  This  cannot  be  considered  very 
exact,  on  account  of  the  difficulty  of  obtaining  the  mother- 
liquor  in  such  a  condition  that  it  neither  dissolves  nor 
deposits  the  substance.  A  sample  of  mother-liquor,  of  specific 
gravity  2.19,  was  found  to  contain  1.61  g.  of  RbI.I2  in  1  c.  c. 
The  compound  therefore  dissolves  in  about  one-third  its 
weight  of  water  at  22°.  It  is  interesting  to  notice  here  that, 
under  nearly  the  same  conditions,  the  corresponding  caesium 
compound,  CsI.I2,  requires  more  than  one  hundred  parts  of 


42  ON  THE  RUBIDIUM  AND 

water  to  dissolve  it.  It  is  expected  that  this  great  difference 
in  solubility  will  form  the  basis  of  a  useful  method  for 
separating  the  two  metals. 

KbBr.BrL 

This  compound  can  be  readily  made  by  dissolving,  with  the 
aid  of  heat,  30  g.  of  iodine  and  20  g.  of  bromine  in  a  saturated 
aqueous  solution  of  40  g.  of  rubidium  bromide  and  cooling. 
The  facility  with  which  this  body  crystallizes  is  remarkable. 
The  large  crystals  have  a  color  and  lustre  much  like  the 
mineral  pyrargyrite,  "  ruby-silver." 


Analysis 

Kubidium  ......     22.79  22.95 

Bromine     ......     45.19  42.95 

Iodine    .......     31.11  34.10 

An  approximate  specific  gravity  determination,  made  with 
the  mother-liquor,  gave  the  number  3.84.  An  analysis  of  the 
mother-liquor  showed  that  it  contained  about  44  per  cent  of 
RbBr.Brl.  The  mother-liquor  of  the  corresponding  caesium 
compound  contained  only  4.45  per  cent  of  CsBr.Brl. 

MCl.BrL 

This  body  can  be  made  by  adding  27  g.  of  bromine  and 
42  g.  of  iodine  to  a  saturated  aqueous  solution  of  40  g.  of 
rubidium  chloride,  warming  until  all  is  in  solution,  and  cool- 
ing. It  forms  magnificent  crystals  which  can  be  readily 
recrystallized  from  water.  Unlike  the  corresponding  caesium 
compound,  it  does  not  change  its  composition  by  recrystalliza- 
tion  ;  hence  it  is  probable  that  it  is  a  true  chemical  compound, 
and  not  a  mixture  of  the  isomorphous  bodies  RbBr.Brl 
and  RbCl.CH. 

Analysis  gave,  Calculated  for 

Original  crystals.    6th  recrystallization.        RbCl.Brl. 

Rubidium  ....  26.67  27.34  26.06 

Chlorine  ....  10.65  .  .  .  10.82 

Bromine  ....  24.89  .  .  .  24.39 

Iodine  38.13  38.72 


POTASSIUM  TRIHALIDES.  43 

RbCLCIL 

A  convenient  method  for  preparing  this  compound  is  to 
pass  chlorine  into  a  warm,  concentrated  solution  of  rubidium 
chloride,  containing  the  calculated  amount  of  iodine,  until  the 
iodine  is  just  dissolved.  If  too  much  chlorine  is  used,  the 
compound  RbCl4I  is  formed,  which  we  shall  describe  in  a 
future  article.  It  is  best  to  stop  adding  chlorine  while  the 
solution  is  still  colored  red  by  iodine.  On  cooling  the  liquid, 
the  compound  separates,  usually  in  large  flat  groups  of  parallel 
crystals. 


Analysis  gave 

Rubidium  ......    29.85  30.15 

Chlorine     ......     24.68  25.04 

Iodine    .  44.68  44.79 


This  can  be  prepared  by  adding  49  g.  of  bromine  to  45  c.  c. 
of  an  aqueous  solution  containing  50  g.  of  rubidium  bromide, 
warming  gently  until  bromine  dissolves,  then  cooling.  It 
usually  forms  a  mass  of  large,  brilliant,  red  crystals  in  parallel 
position. 


Analysis  gave 

Rubidium  ......     25.86  26.26 

Bromine     ......     73.09  73.73 


This  body  is  prepared  by  adding  bromine  to  a  warm,  satu- 
rated solution  of  rubidium  chloride  until  some  bromine 
remains  undissolved,  and  cooling  to  a  low  temperature.  The 
compound  crystallizes  well,  but  it  is  the  most  unstable  of  the 
seven  rubidium  trihalides  that  have  been  prepared,  and, 
although  it  was  not  fully  dried,  the  sample  used  for  analysis 
suffered  a  considerable  amount  of  decomposition. 


44  ON   THE  RUBIDIUM  AND 


Analysis  gave 

Kubidiuin   ....     32.57  .  .  .  30.42 

Chlorine     ....     14.46  14.44  12.63 

Bromine      ....     49.04  49.40  56.93 

In  one  attempt  to  prepare  this  trihalide  too  much  water  was 
used,  and  it  was  necessary  to  evaporate  off  the  bromine  and 
concentrate  the  solution.  This  operation  was  repeated  several 
tunes,  after  fresh  additions  of  bromine,  before  the  proper  con- 
ditions were  arrived  at,  and  the  product  finally  obtained  was 
contaminated  with  RbBr.Br2,  as  is  shown  by  the  following 
analyses  : 

Wnnnd  Calculated  for        Calculated  for 

RbCl.Br2.  RbBr.Brj. 

Kubidium   .     .     .     28.78         .  .  .         30.42  26.26 

Chlorine     .     .     .       7.66          6.94        12.63  0. 

Bromine      .     .    .     60.92        61.37        56.93  73.73 

We  have  found  by  experiment  that  rubidium  chloride  is 
partly  changed  to  bromide  by  evaporating  an  aqueous  solution 
of  it  with  bromine.*  This  explains  the  formation  of  the 
RbBr.Br2. 

EbCl.ClBr. 

This  compound  can  be  prepared  by  adding  33  g.  of  bromine 
to  a  saturated  solution  of  50  g.  of  rubidium  chloride,  passing 
chlorine  to  saturation  into  the  slightly  warmed  solution,  and 
cooling  to  a  low  temperature.  The  substance  is  usually 
deposited  in  the  form  of  very  large,  light  yellow  prisms. 

A     ,     .    ^  Calculated  for 

Analysis  gave  RbCl.ClBr. 

Rubidium   ....    35.42  35.41  36.15 

Chlorine      ....     29.27  28.96  30.02 

Bromine      ....    31.56  31.39  33.82 

KLI*. 

This  body  can  be  made  in  a  few  hours  by  dissolving  the 
theoretical  amount  of  iodine  in  a  hot,  saturated,  aqueous  solu- 

*  This  is  in  accordance  with  the  results  of  Potilzin  referred  to  by  Men- 
dele'eff  in  his  "Grundlagen  der  Chemie"  (German  ed.,  1891),  p.  638. 


POTASSIUM  TRIHALIDES.  45 

tion  of  potassium  iodide  and  exposing  the  resulting  solution  to 
a  winter  temperature.  It  can  also  be  made,  as  Johnson  states,* 
by  evaporating  the  solution  in  a  desiccator  for  a  long  time. 
Johnson  states  that  he  always  obtained  a  crop  of  potassium 
iodide  before  the  triiodide  separated.  We  have  never  obtained 
such  a  product,  undoubtedly  because  we  have  invariably  used 
a  sufficient  amount  of  iodine. 

It  was  not  considered  necessary  to  make  a  new  analysis  of 
this  body. 

KBr.BrL 

This  compound  can  be  prepared  by  making  a  very  concen- 
trated, warm  solution  of  the  calculated  amounts  of  potassium 
bromide,  bromine,  and  iodine,  and  exposing  it  for  some  time  to 
a  low  temperature.  The  product  used  for  analysis  was  well 
crystallized,  but  it  suffered  rapid  decomposition  on  exposure 
to  the  air. 

Analysis  gave  ^Srl^ 

Potassium  ....     12.21  .  .  .  11.99 

Bromine      ....     51.25  51.61  49.06 

Iodine 30.42  29.11  38.94 

KCl.CIL 

To  prepare  this  substance,  chlorine  is  passed  into  a  warm 
mixture  of  calculated  quantities  of  potassium  chloride  and 
iodine,  in  the  presence  of  an  amount  of  water  insufficient  to 
dissolve  the  potassium  chloride  even  when  hot.  The  stream 
of  chlorine  is  stopped  as  soon  as  the  iodine  has  been  converted 
into  the  monochloride,  for  otherwise  Filhol's  well-known  com- 
pound KC1.C13I  will  be  formed.  Everything  is  then  dis- 
solved by  warming  and  cautiously  adding  water  if  necessary, 
and  the  solution  is  exposed  to  a  low  winter-temperature.  The 
crystals  are  very  unstable,  but  apparently  not  quite  as  much  so 
as  KBr.BrL 

Analysis  gave  0*$88&a 

Potassium  ....     15.29  15.35  16.49 

Chlorine     ....    27.53  27.50  29.94 

Iodine 50.37  50.12  53.56 

*  Loc.  cit. 


46  ON  THE  RUBIDIUM  AND 

Other  Double  Halides. 

The  double  salt  CsI.AgI  was  described  in  connection  with 
the  caesium  trihalides  as  being  isomorphous  with  them  as  far 
as  the  crystals  could  be  measured.  Much  work  has  since  been 
done,  without  avail,  in  the  hope  of  obtaining  better  crystals  of 
this  compound.  Unsuccessful  efforts  have  been  made  to 
obtain  measurable  crystals  of  all  the  corresponding  silver 
double  halides  (except  the  fluorides)  with  caesium,  rubidium, 
and  potassium.  Two  or  three  of  these  compounds  had  already 
been  described,  and  it  is  probable  that  we  could  have  proven 
the  existence  of  all  the  rest  of  them,  but  the  poorly  crystal- 
lized products  obtained  had  no  interest  in  this  connection  and 
were  not  analyzed.  Repeated  efforts  also  failed  to  produce 
from  potassium  iodide  and  cuprous  iodide  a  double  salt  that 
could  be  measured. 

Theoretical. 

Arguments  were  given  in  the  article  on  the  caesium  series 
which  have  led  us  to  regard  the  trihalides  as  belonging  to  the 
class  of  bodies  called  double  halides.  We  have  indicated  this 
view  in  the  present  article  by  using  the  usual  formulae  for 
such  compounds. 

The  well-known  idea  of  a  linking  group  of  two  halogen 
atoms  as  an  explanation  of  the  structure  of  double  halides  was 
advocated  for  the  caesium  trihalides,  and,  since  the  rubidium 
and  potassium  compounds  are  entirely  analogous,  it  is  unneces- 
sary to  give  their  structural  formulae  here.  We  believe,  how- 
ever, that  the  trihalides  throw  some  light  upon  the  constitution 
of  the  diatomic  linking  group.  Remsen  says,*  "  I  cannot  see 
that  at  present  we  have  any  evidence  which  justifies  us  in  the 
use  of  the  expression  —  C1  =  C1—  rather  than  —  Cl  —  Cl— ." 
If,  as  we  believe,  the  structure  of  rubidium  triiodide  is  ex- 
pressed by  the  formula  Rb  —  (II)  —  I,  the  structure  of  the  link- 
ing group  probably  cannot  be  —  I  —  I— ;  for  in  that  case  a 
single  bivalent  iodine  atom  could  do  the  linking  as  well  as  a 
group  of  two,  and  we  should  expect  the  existence  of  diiodides, 

*  Araer.  Chem.  Jour.,  xi,  312. 


POTASSIUM  TRIHALWES.  47 

no  evidence  of  which,  or  of  any  other  dihalide,  has  been  found 
in  the  course  of  an  elaborate  investigation  of  the  alkali-metal 
polyhalides.  Moreover,  with  the  assumption  of  bivalent  halo- 
gen atoms,  there  would  be  no  difficulty  in  supposing  four 
halogens  to  be  linked  together,  and  the  existence  of  tetra- 
halides  would  be  anticipated.  Our  investigations,  however, 
have  shown  the  existence  of  only  tri-  and  pentahalides.*  The 
double  linking  seems  therefore  the  more  probable  of  the  two 
forms  mentioned  by  Remsen,  but  it  may  be  added  that  any 
union  weaker  or  stronger  than  the  others  in  the  molecule,  and 
different  from  them,  would  also  explain  the  non-existence  of 
dihalides  and  tetrahalides. 

Assuming  that  there  is  a  linking  group  of  two  halogen 
atoms  in  the  trihalides,  the  view  advanced  from  a  considera- 
tion of  the  caesium  compounds,  that  the  most  stable  bodies 
have  identical  atoms  in  this  group,  is  confirmed  by  the  study  of 
the  rubidium  and  potassium  analogues.  For,  on  this  assump- 
tion, all  the  potassium  compounds  which  could  be  made  con- 
tain a  group  of  identical  atoms,  while  in  the  missing  rubidium 
compound  they  are  dissimilar. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
March,  1892. 

*  The  pentahalides  will  be  described  in  a  future  article. 


ON  THE  ALKALI-METAL  PENTAHALIDES.* 

BY  H.  L.  WELLS  AND  H.  L.  WHEELER. 

WITH  THEIR,   CRYSTALLOGRAPHY. 

BY  S.  L.  PENEIELD. 

IN  the  course  of  our  investigations  on  the  alkaline  trihalides,f 
the  compounds  CsCl.ClJ,  RbCl.Cl3I,  and  KC1.C13I  were 
encountered.  The  potassium  compound  had  been  described 
many  years  ago  by  Filhol.J  This  investigator  prepared  also 
the  body  NH4C1.C18I  and  obtained  a  similar  magnesium 
compound,  probably  MgCl2.2Cl8I.5H2O.  He  failed  in  his 
attempts  to  make  analogous  compounds  with  sodium  and  a 
considerable  number  of  the  other  common  metals. 

It  was  evident  from  the  peculiar  behavior  of  caesium  tribro- 
mide  and  triiodide,  mention  of  which  was  made  in  one  of  our 
previous  articles,  §  that  a  still  higher  bromide  and  iodide 
existed.  These  have  now  been  identified  as  pentahalides. 

In  addition  to  these  bodies,  we  have  prepared  the  sodium 
and  lithium  analogues  of  Filhol's  salt.  They  differ  from  all 
the  other  polyhalides  that  we  have  studied,  in  containing  water 
of  crystallization. 

A  large  number  of  other  alkaline  pentahalides  are  theoreti- 
cally possible,  but,  although  we  have  made  numerous  experi- 
ments with  the  view  of  making  the  most  promising  of  these, 
we  have  been  unable  to  prepare  them.  It  may  be  stated  that 
special  efforts  were  made  to  obtain  potassium  and  rubidium 
pentaiodides. 

*  Amer.  Jour.  Sci.,  xliv,  July,  1892. 

t  Ibid,  III,  xliii,  17  and  475. 

J  J.  Pharm.,  xxv  (1839),  431. 

§  Amer.  Jour.  Sci.,  Ill,  xliii,  24  and  27. 


ALKALI-METAL  PENTAHALIDES. 


49 


This  is  produced,  in  an  impure  state  as  a  black  liquid  solidi- 
fying at  about  73°,  by  treating  caesium  triiodide  with  hot 
water,  and  also  by  treating  solid  iodine  with  a  hot  solution  of 
caesium  iodide.  Artificial  mixtures  of  caesium  triiodide  and 
iodine,  representing  compositions  varying  from  CsI4  to  CsI9, 
all  melt  at  a  uniform  temperature  of  about  73°.  It  is  evident 
from  this  that  the  composition  of  the  black  liquid  cannot  be 
determined  from  its  melting-point. 

Csesium  triiodide,  which  is  readily  soluble  in  alcohol,  be- 
comes much  more  soluble  in  that  liquid  in  the  presence  of  two 
atoms  of  iodine  to  the  molecule.  A  very  concentrated  solu- 
tion of  this  kind  gives  crystals  of  the  pentaiodide  by  cooling, 
but  a  much  better  product  is  obtained  by  concentration  over 
sulphuric  acid,  using  a  slight  excess  of  iodine  to  allow  for  loss 
by  volatilization.  The  crystals  are  well  formed  and  have  a 
brilliant  black  color.  They  can  be  distinguished  from  crystals 
of  iodine,  which  may  separate  if  too  much  of  this  substance 
has  been  used,  by  their  brittleness  as  well  as  their  form.  The 
substance  melts,  not  sharply,  at  73°.  It  loses  iodine  on  expo- 
sure about  as  rapidly  as  iodine  itself  volatilizes.  It  does  not 
contain  water  or  alcohol. 

Samples  of  the  crystals  quickly  dried  wiiji  paper  gave  the 
following  results  on  analysis : 


Caesium 
Iodine 


Made  by 
cooling. 

15.20 


By  evaporation. 
Separate  products. 

20.96        16.02 


Calculated 
for  CsI5. 

17.32 
82.68 


When  a  concentrated  solution  of  caesium  bromide  is  shaken 
up  with  a  large  excess  of  bromine,  there  is  no  separation  of 
caesium  tribromide,  as  is  the  case  when  the  theoretical  amount 
of  bromine  is  used.  A  large  part  of  the  caesium  bromide 
goes  into  solution  in  the  liquid  bromine  and,  on  taking  up  a 
sufficient  quantity  of  caesium  bromide,  this  solution  becomes 
lighter  in  color  than  pure  bromine. 

4 


50  ON  THE  ALKALI-METAL 

A  solution  of  caesium  bromide  in  bromine,  made  in  the 
manner  above  indicated,  was  allowed  to  evaporate  spontane- 
ously at  a  temperature  below  0°.  A  dark  red  solid  finally 
separated,  and  it  was  prepared  for  analysis  by  pressing  with 
papers  at  the  same  low  temperature.  After  the  adhering 
bromine  had  been  removed,  the  substance  gave  off  bromine- 
vapor  very  rapidly. 

Analysis  gave  g^gg 

Caesium 29.93  24.95 

Bromine 75.05 

The  analysis  corresponds  with  the  formula  CsBr5  as  well  as 
could  be  expected,  considering  the  great  instability  of  the 
compound. 

CsCLClJ. 

This  substance  can  be  prepared  by  dissolving  40  g.  of 
caesium  chloride  in  a  mixture  of  600  c.  c.  of  water  and  200 
c.  c.  of  concentrated  hydrochloric  acid,  adding  30  g.  of  iodine 
(one  atom),  and  passing  chlorine  to  saturation;  meanwhile 
keeping  the  solution  warm  enough  to  dissolve  any  of  the 
compound  which  separates  in  the  form  of  a  yellow  precipitate, 
and  finally  cooling  to  crystallization.  The  hydrochloric  acid 
is  used  to  prevent  the  simultaneous  deposition  of  an  acid 
caesium  iodate. 

Analysis  gave          *$%$?* 

Caesium 32.44  33.09 

Chlorine 34.79  35.32 

Iodine 31.11  31.59 

The  crystals  are  of  a  pale  orange  color.  They  are  in  the 
form  of  slender  prisms,  usually  in  parallel  position  forming 
plate-like  groups.  The  body  is  sparingly  soluble  in  water  and 
can  be  recrystallized  from  it  without  much  decomposition.  It 
is  nearly  permanent  in  the  air.  On  heating,  it  is  apparently 
converted  into  CsCl.CH,  for  it  melts  like  that  substance  at 
238°  (uncorr.)  in  the  open  capillary  tube. 


PENTAHALIDES,  51 

RbCLCZ  J. 

This  body  can  be  conveniently  prepared  by  adding  40  g. 
of  iodine  to  a  nearly  saturated  solution  of  38  g.  of  rubidium 
chloride  and  passing  in  an  excess  of  chlorine.  The  solution 
becomes  warm  from  the  reaction  and,  on  cooling,  large  orange- 
yellow  plates  are  deposited. 


Analysis  gave 

Eubidium    ....     24.12        23.63  24.11 

Chlorine      ....     39.00          .  .  .  40.05 

Iodine    .....     35.31         .  .  .  35.83 

The  compound  is  soluble  in  alcohol,  but  unaffected  by  ether. 
When  rapidly  heated  in  an  open  capillary  tube,  it  melts  at 
213°  (uncorr.),  undergoing  some  decomposition,  and  becomes 
completely  white  at  about  270°.  These  numbers  agree  quite 
closely  with  the  melting  and  whitening  points  of  RbCl.ClI, 
so  that  it  is  evident  that  there  is  a  loss  of  two  atoms  of  chlo- 
rine before  much  further  decomposition  takes  place.  In  view 
of  this  fact,  it  is  remarkable  that,  when  samples  of  RbCl.Cl3I 
and  RbCl.CU  were  exposed  to  the  air  side  by  side  for  three 
months,  the  compound  containing  the  greater  amount  of 
chlorine  was  almost  completely  decomposed,  while  the  other 
remained  nearly  unchanged.  It  is  therefore  probable  that 
RbCl.Cl3I  decomposes  at  ordinary  temperatures  by  losing 
C18I  as  a  whole,  while  by  heating  another  decomposition 
takes  place. 


This  compound,  first  described  by  Filhol,  has  been  prepared 
for  the  sake  of  studying  its  crystalline  form.  It  is  easily  made 
by  the  method  which  has  been  given  for  the  corresponding 
rubidium  compound.  The  crystals  obtained  by  cooling  are 
in  the  form  of  very  slender  needles,  but,  by  evaporating  the 
mother-liquor  from  these  at  ordinary  temperature,  thicker 
prisms  suitable  for  measurement  can  be  obtained. 


52  ON  THE  ALKALI-METAL 


Analysis  gave 

Potassium 11.98  12.66 

Chlorine 45.31  46.10 

Iodine 42.50  41.23 

NaCl.CUZHtO. 

To  prepare  this  substance,  sodium  chloride  and  iodine,  in 
the  calculated  proportions,  are  mixed  with  an  amount  of  water 
insufficient  to  dissolve  the  sodium  chloride  even  on  heating, 
chlorine  is  added  to  saturation  at  a  gentle  heat,  and  the  liquid 
is  filtered  while  still  warm.  The  solution,  on  cooling  to  a  low 
winter  temperature,  gives  a  crop  of  slender  needles,  but  better 
crystals  are  obtained  by  evaporation  in  a  desiccator.  Some 
of  the  latter,  quickly  dried  on  paper,  gave  the  following  results 
on  analysis  : 

fpnnnA  Calculated  for 

NaCl.Cl3L2H2O. 

Sodium 7.17  7.01 

Chlorine 42.92  43.29 

Iodine 38.23  38.71 

Water 12.84*  10.97 

The  water  was  determined  by  direct  weighing  in  a  calcium 
chloride  tube,  the  halogens  being  retained  by  an  ignited  mix- 
ture of  lead  oxide  and  lead  chromate. 

The  body  is  rapidly  decomposed  by  exposure.  It  melts 
gradually  between  70°  and  90°  and  becomes  white  at  about 
115°.  It  is  decomposed  by  strong  alcohol  and  by  ether. 

LiCl.ClJ.4HiO. 

This  was  made  by  adding  60  g.  of  iodine  to  a  hot  saturated 
solution  of  20  g.  of  lithium  chloride  in  dilute  hydrochloric 
acid,  saturating  with  chlorine  and  cooling.  A  large  quantity 
of  long  yellow  needles  was  thus  obtained.  On  evaporating 
the  mother-liquor  in  a  desiccator,  larger  prisms  were  deposited. 

*  Determined  in  a  separate  sample. 


PENTAHALIDES. 


53 


Analysis  gave 

Lithium 2.03  2.16 

Chlorine 39.96  39.94 

Iodine 37.54  36.77 

Water  .  20.93 


Calculated  for 
LiCl.Cl3I.4HjO. 

2.01 

40.80 
36.49 
20.68 


On  exposure  to  the  air  the  substance  quickly  deliquesces, 
forming  a  yellow  liquid.  This  gradually  loses  its  color,  finally 
leaving  a  solution  of  lithium  chloride.  The  body  melts  at 
70-80°  and  becomes  white  at  about  180°.  The  crystals  of 
this  compound  were  not  measured. 

Crystallography. 

The  crystallization  of  CsI5  is  triclinic.  By  slow  evaporation 
of  solution  in  a  desiccator,  crystals  were  obtained  which  were 
about  10  mm.  in  diameter.  Two  crops  were  examined,  in  one  of 
which  the  habit  shown  in  Fig.  1  prevailed,  while  in  the  second 
the  crystals  were  more  highly  modified,  like  Figs.  2  and  3. 


The  forms  which  were  observed  are : 

HP 


a,  100,  i-i 

c,  001,  0 

m,  110,  1' 

M,  1TO,  / 


d,  on, 

/,  041,     4^' 
6,  021,     2-i 
PJ  311,  -3-3' 


0,  311,  3-3' 
x,  341,  -4-|' 
y,  341,  4-|' 


The  axial  ratio  is  as  follows : 

£  :  I  :  c  =  0.9890  ;  1  :  0.42765 
a  =  96°  56'  ft  =  89°  55V  7  =  90°  21  y 


54 


ON   THE  ALKALI-METAL 


The  crystals  gave  good  reflections  of  the  signal  on  the  goni- 
ometer. In  the  following  tables  the  measurements  which 
were  chosen  as  fundamental  are  indicated  by  an  asterisk : 


a 
m 
a 
c 
e 
a 
a 
a 
a 
a 

AC, 
AM, 
A  m, 
A  e, 
Arf, 
AM, 
AC, 

Ad, 
A/?, 
AO, 

100  A  001 

no  A  no 

100  A  110 
001  A  021 
021  A  Oil 
100  A  110 
100  A  021 
100  A  Oil 
100  A  311 
100  A  311 

Measured. 
=  *90°  2' 
=  *89°  47' 
-  *44o  43' 

-  *43°  26' 
=  *65°  25' 
=  45°  4' 
=  90°  6' 
=  89°  57' 
=  41°  18' 
=  41°  31' 

Calculated. 

45°  4' 
90°  16' 
89°  54' 
41°  19' 
41°  25' 

c 
c 
e 
e 
d 
d 
P 
/ 

X 

y 

A  TO, 
AM, 
A  TO, 
AM, 
A  TO, 
AM, 
A  TO, 
AC/, 
A  TO, 
AM, 

001 
001 
021 
021 
Oil 
Oil 
311 
041 
341 
B41 

Measured. 
A  110  =  85°  8' 
A  110  =  85°  7' 
A  110  =  65°  9' 
A  HO  =  65°  8' 
A  110  =  70°  3' 
A  HO  =  70°  & 
A  110  =  40°  41' 
A  Oil  =  32°  3V 
A  110  =  25°  46' 
A  110  =  25°  56' 

Calculated. 
85°  9' 
85°  7f 
65°  3' 
65°  18' 
70°  2' 
70°  4X 
40°  41' 
32°  37£' 
25°  44|' 
25°  52' 

The  form  of  CsCl.Cl8I  is  monoclinic.  From  a 
number  of  crystallizations  this  salt  was  always  ob- 
tained in  needles,  sometimes  over  20  mm,  in  length 
and  having  the  habit  shown  in  Fig.  4. 

The  forms  which  were  observed  are : 


b,   010,   i-l 
I,   210,  t-2 


p,  212,  —1-2 
q,  211,  -2-2 


s,   211,  2-2 
d,  041,    4-T 


The  axial  ratio  is  as  follows  : 


a:b:c  =  0.9423  :  1  :  0.4277,  0  =  100  A  001  =  86°  20' 


Measured.       Calculated. 
I  A  I,  210  A  210  =    *50°  22' 
I  A  p,  210  A  212  =    *44°  61' 
p  A  s,  212  A  2fl  =  *106°  35' 
/  A  q,  210  A  211  =     27°    3'        27°  T 


Measured.  Calculated. 

I  A  s,  210  A  2fl  =  28°  35'  28°  34' 

p  A  p,  212  A  212  =  32°  59'  33°    2' 

p  A  b,  212  A  010  =  73°  31'  73°  29' 

b  A  rf,  010  A  041  =  31°    0'  30°  21' 


The  crystallization  of  RbCLClJ  is 
monoclinic.  This  salt  was  crystallized  a 
great  many  times,  and  was  always  ob- 
tained in  plates,  sometimes  over  20  mm. 
broad,  but  seldom  1  mm.  thick.  The 
habit  is  shown  in  Fig.  5. 

The  forms  which  were  observed  are : 


PENTAHALIDES.  55 

b,  010,   i-i  m,   110,     1  s,   Til,    1 

c,  001,  0  /?,   Ill,  -1 

The  axial  ratio  is  as  follows  : 

a  :  b  :  c  =  1.1390  :  1  :  1.975,   ft  =  100  A  001  =  67°  6J> 

Measured.  Measured.  Calculated. 

c  A  m,  001  A  110  =  *74°  26'  CAS,  001  A  111  =  82°  12'  82°  15' 

CAP,  001  A  111  =  *55°  20'  s  A  m,  111  A  110  =  23°  207  23°  19' 

,  111  A  111  =  *76°  21'  />A  TO,  111  A  110  =190    5'  19°    6' 


With  the  polarizing  microscope  the  plates  show  an  extinc- 
tion parallel  to  their  diagonals.  In  convergent  light  nothing 
of  the  ring  system  can  be  seen,  but  a  dark  bar  crosses  the 
field  in  the  direction  of  the  symmetry  plane,  indicating  that 
the  plane  of  the  optical  axes  is  the  clino-pinacoid. 

The  crystalline  habits  and  axial  ratios  of  CsCl.Cl3I  and 
RbCl.Cl3I  are  wholly  different,  and  all  attempts  to  find  any 
similarity  or  mathematical  relation  between  them  has  failed. 
We  have  endeavored  to  detect  any  hidden  relation  that  might 
exist  by  examining  separate  crops  of  crystals,  made  from  a 
solution  containing  both  salts.  Each  form  alone  and  mixtures 
of  both  were  thus  obtained,  but  no  crystals  of  an  intermediate 
form  could  be  produced.  One  unmixed  crop,  having  the 
form  and  angles  of  CsCl.Cl3I,  contained  about  sixteen  per 
cent  of  RbCl.Clgl,  while  another,  having  the  form  and 
angles  of  RbCLClat,  contained  about  eleven  per  cent  of 
CsCl.Cl3I.  These  results  show  that  isomorphous  mixtures 
can  be  obtained  of  either  form,  depending  upon  which  salt 
predominates,  while  the  absence  of  any  intermediate  forms, 
and  the  inability  to  detect  any  mathematical  relation  between 
the  two  kinds  of  crystals,  lead  us  to  believe  that  the  com- 
pounds are  dimorphous. 

The  form  of  KCl.CLJ  is  monoclinic.  This  salt  was  re- 
peatedly made  in  fine  needle-like  crystals,  too  small  to  meas- 
ure, by  allowing  a  warm  saturated  solution  to  crystallize. 
By  slow  evaporation  in  a  desiccator,  at  ordinary  temperatures, 
stouter  prismatic  crystals,  over  20  mm.  long  and  2  mm.  in 


56 


ON  THE  ALKALI-METAL 


6. 


diameter  were  obtained,  having  the  habit  shown 
JJ_         in  Fig.  6.     These  gave   excellent  reflections  and 
were  measured  without  difficulty  at  winter  temper- 
ature. 

The  forms  which  were  observed  are : 


a,  100,  i-i 
m,   110,  / 


nt   120,  t-2 
d,   023,  f-r 


The  axial  ratio  is  as  follows  : 
a:b:c  =  0.9268  : 1 :  0.44725,  0  =  100  A  001  =  84°  18' 


Measured. 

roA>n,  110AlTO  =  *85°22' 
d  A  d,  023  A  023  =  *33°    3' 


Measured.      Calculated, 
a  A  d,  100  A  023  =  *84°  32' 
n  A  n,  120  A  120  =    56°  58'        66°  56' 


The  positions  and  crystal  symbols  which  have  been  adopted 
for  this  and  the  corresponding  caesium  salt  were  chosen  to 
show  a  similarity  in  the  axial  ratios.  Both  salts  are  alike  in 
having  a  prismatic  habit,  but  the  forms  which  occur  on  each 
are  quite  different.  If  it  were  not  for  bringing  out  this  simi- 
larity in  axial  ratios,  the  crystallography  of  both  salts  could 
be  simplified  somewhat  by  giving  to  the  dome  d  above  the 
simpler  indices  Oil,  and  by  taking  the  prism  and  pyramids 
of  the  caesium  salt  as  belonging  to  the  unit  instead  of  to  the 
macrodiagonal  series. 

The  anhydrous  alkali-metal  pentahalides  do  not  form  a 
well-defined  crystallographic  series,  yet  there  are  relations 
between  three  of  them  which  seem  to  us  to  be  more  than 
coincidences.  The  similarity  is  shown  in  the  following 
table: 

CsCLClgl  Monoclinic  a  :  b  :  c  =  0.9423  :  1  :  0.4277,    ft  =  86°  20' 
KC1.C13I  "  a  :  b  :  c  =  0.9268  :  1  :  0.44725,  ft  =  84°  18' 

T  -nr  •«  5  *  :  *  :  «  =  °-9890  :  *  :  0.42765 
Tnchmc       =  %0  ^     =  8 


PENTAHALIDES. 


57 


The  crystallization  of  NaCl.Cl3I.2H2O  is  ortho- 
rhombic.  By  slow  evaporation  of  a  solution  in  a 
desiccator,  crystals  were  formed  over  10  mm.  in 
length,  having  the  habit  shown  in  Fig.  7. 

The  forms  which  were  observed  are : 


b,  010,  i-i 
m,   110,  / 


A   HI,   1 

d,  021,  2-i 


m 


7. 


771 


The  axial  ratio  is  as  follows  : 

a:b:c  =  0.6745  :  1  :  0.5263 


The  crystals  were  measured  at  a  temperature  near  0°  C. 
and  gave  excellent  reflections. 

Measured.  Measured.     Calculated. 

m  A  m,  110  A  110  =  *68°  0'    m  A  b,  110  A  010  =  56°  (X   66°  0' 
m  A  p,  110  A  111  =  *46°  44'    6  A  d,  010  A  021  =  43°  2^   43°  32' 


SHEFFIELD  SCIENTIFIC  SCHOOL, 
April,  1892. 


ON  SOME  ALKALINE  IODATES.* 

BY   H.  L.   WHEELER. 

WITH  CKYSTALLOGKAPHIC  NOTES. 
BY  S.  L.   PENFIELD. 

WHILE  work  on  the  compounds  of  iodine  trichloride  with 
alkaline  chlorides  f  was  in  progress  in  this  laboratory,  it  was 
noticed  in  making  K1C.C1J,  RbCl.Cl3I,  and  CsCl.CU  that 
white  crystals  were  often  formed  under  certain  conditions. 
These  compounds  proved  to  be  KC1.KIO8.HIO3,  RbCl.HIO8, 
and  2CsIO8.I2O6.  Since  they  were  not  analogous,  although 
formed  under  similar  conditions,  and  since  the  rubidium  and 
caesium  salts  have  not  been  described,  an  investigation  of  them 
was  undertaken.  Attempts  to  prepare  these  compounds  by 
other  methods  led  to  the  discovery  of  several  other  iodates. 
The  new  compounds  that  have  been  prepared  are  as  follows  : 

KbI03  CsI03 

KbI03.HI03  2CsI03.I205 

KbI03.2HI03  2CsI03J205.2HI03 

KbCl.HIOs  CsCl.HIOs 
3KbC1.2HI03 

The  compound  which  separated  from  the  solution  of  the 
potassium  pentahalide  has  already  been  described,  but  since  this 
is  a  new  method  of  preparation,  and  since  there  are  conflicting 
statements  concerning  its  state  of  hydration,  it  has  been  re- 
investigated. 

The  results  of  the  investigation  of  the  rubidium  salts  show 
that  the  normal  iodate  is  the  only  one  of  the  series  that  can  be 
recrystallized  unaltered  from  an  aqueous  solution.  In  the 

*  Amer.  Jour.  Sci.,  xliv,  August,  1892.  t  Ibid.,  p.  42. 


ON  SOME  ALKALINE  IODATES. 


59 


case  of  the  csesium  compounds,  the  normal  iodate  and  the  salt 
2CsIO3.I2O5  are  not  decomposed  by  water.  The  other  caesium 
iodates  give  2CsIO3.I2O5  when  recrystallized  from  water,  and 
not  the  normal  iodate,  thus  showing  an  interesting  difference 
between  the  rubidium  and  caesium  compounds. 

It  is  the  tendency  of  the  acid  rubidium  iodates  to  separate 
in  a  higher  state  of  hydration  than  the  corresponding  csesium 
compounds. 

It  is  also  an  interesting  fact  that  the  formation  of  the  com- 
pounds of  normal  chloride  and  iodic  acid  was  not  observed  on 
mixing  the  constituents.  In  the  case  of  rubidium,  products 
were  obtained  which  proved  to  be  RbIO3,  RbIO3.HIO3,  or 
RbIO3.2HIO3,  according  to  the  concentration  of  the  solutions 
and  the  excess  of  RbCl  or  HIO3.  On  the  other  hand,  by  add- 
ing hydrochloric  acid  to  a  solution  of  rubidium  iodate,  if  the 
acid  is  dilute  RbIO3.2HIO3  is  formed,  while  if  concentrated  the 
iodate  is  completely  decomposed.  Similar  experiments,  under- 
taken with  caesium  chloride  and  iodic  acid,  did  not  give  the 
peculiar  double  compound  CsCl.HIO3,  but  resulted  in  each 
case  in  the  formation  of  2CsIO3.I2O5. 

Method  of  Analysis.  —  After  the  substances  were  prepared 
for  analysis  as  described  in  detail  beyond,  the  halogens  were 
determined  by  first  reducing  the  solution  of  iodate  with  sul- 
phur dioxide,  then  precipitating  with  silver  nitrate  in  the 
presence  of  nitric  acid.  This  precipitate  was  then  heated  in 
a  stream  of  chlorine,  thus  combining  the  test  for  chlorine  and 
its  determination  in  one  operation.  In  the  filtrate  from  the 
silver  precipitate,  the  alkali  metal  was  determined  as  sulphate 
after  the  removal  of  the  excess  of  silver  by  means  of  hydrogen 
sulphide.  Oxygen  was  determined  in  a  separate  portion  by 
precipitation  with  silver  sulphate,  drying  the  precipitate  at 
100°,  and  then  determining  the  loss  on  ignition.  Duplicate 
halogen  determinations  were  then  made  in  this  residue.  In 
the  case  of  the  compounds  containing  the  group  I2O3,  where 
an  error  would  be  introduced  if  the  oxygen  was  determined 
in  this  manner,  the  substance  itself  was  ignited  and  the  oxygen 
calculated  from  the  loss.  The  presence  of  water  in  these  com- 


60  ON  SOME  ALKALINE  IODATES. 

pounds  was  determined  by  directly  weighing  it  in  a  calcium- 
chloride  tube,  the  substance  being  ignited  in  a  combustion 
tube  containing  a  mixture  of  lead  chromate  and  lead  oxide. 

Normal  Rubidium  lodate,  RHO*.  —  This  compound  was 
made  by  adding  one  molecule  of  iodine  pentoxide  in  either 
strong  or  dilute  aqueous  solution,  to  a  solution  of  one  mole- 
cule of  rubidium  carbonate.  If  the  solutions  are  strong  the 
iodate  separates  as  a  sandy  precipitate,  but  if  they  are  hot  and 
dilute  it  separates  on  cooling  in  small  grains  or  as  a  crystalline 
crust.  At  23°,  100  parts  of  water  dissolve  2.1  parts  of  the 
salt.  The  compound,  after  filtering  on  the  pump,  washing 
with  a  little  water  and  drying  on  paper,  gave  the  following 
results  on  analysis  : 

Found.  Calculated  for  RbIOs. 

Eubidium 32.17  32.82 

Iodine 48.50  48.75 

Oxygen 20.59  18.43 

The  salt  decrepitates  strongly  when  heated,  then  melts,  gives 
off  oxygen  but  no  iodine,  and  the  residue  is  rubidium  iodide. 
Hydrochloric  acid  readily  dissolves  it  in  the  cold  to  a  faint 
yellow-colored  solution  which  increases  in  color  on  standing. 
On  warming,  chlorine  is  evolved  and  the  solution  turns  bright 
yellow  from  the  formation  of  iodine  trichloride.  If  boiled 
with  strong  hydrochloric  acid,  RbCl.ClI  *  is  formed,  which 
separates  on  cooling. 

The  formation  of  normal  rubidium  iodate  was  also  observed 
when  a  hot  dilute  aqueous  solution  of  iodine  trichloride  was 
treated  with  rubidium  carbonate.  The  compound  thus  ob- 
tained gave  48.43  per  cent  of  iodine  on  analysis.  It  was 
formed  also  by  dissolving  the  acid  iodate  in  a  strong,  hot  solu- 
tion of  rubidium  chloride,  and  allowing  the  mixture  to  crys- 
tallize. This  was  identified  by  a  rubidium  determination 
which  gave  32.58  per  cent.  In  general,  the  iodates  of  rubid- 
ium all  give  this  body  when  they  are  dissolved  in  hot  water 
and  the  solutions  left  to  crystallize.  The  products  obtained 

*  Amer.  Jour.  Sci.,  xliii,  475. 


ON  SOME  ALKALINE  IODATES. 


61 


in  this  manner  decrepitated  on  heating  and  did  not  give  off 
iodine.  A  rubidium  determination  in  the  substance  obtained 
from  RbCl.HIOs  gave  32.76  per  cent;  from  3RbC1.2HIO8, 
32.22  per  cent. 

Acid  Rubidium  lodate,  RbIOz.HIOy  —  This  was  obtained  by 
mixing  warm  solutions  of  one  molecule  of  iodine  pentoxide 
and  two  molecules  of  rubidium  chloride.  The  compound 
generally  separates  on  cooling  as  a  heavy  crystalline  powder. 
It  is  difficultly  soluble  in  cold  water.  Hot  water  dissolves  it 
more  readily,  and  on  cooling  the  normal  iodate  separates.  It 
is  insoluble  in  alcohol.  The  crystals  were  filtered  on  a  pump 
and  washed  with  a  little  cold  water  and  then  pressed  on  paper. 
An  analysis  of  these  dried  at  100°  gave  the  following  results, 
the  oxygen  being  determined  by  difference. 


Found. 

Rubidium 20.13 

Iodine 58.12 

Oxygen 21.46 

Hydrogen 0.29 


Calculated  for  RbI03.HI03. 
19.58 

58.19 

21.99 

0.23 


The  reaction  which  takes  place  in  the  preparation  of  this 
compound  is  probably  according  to  the  following  equation: 

RbCl  +  2HIO3  =  RbI08.HIOa  +  HC1 

The  hydrochloric  acid  thus  liberated  reacts  on  a  part  of  the 
iodic  acid,  chlorine  is  evolved,  and  the  solution  becomes 
yellow.  When  heated  it  does  not  decrepitate,  but  melts  to 
a  yellow  mass,  gives  off  water,  then  iodine,  and  finally  froths 
with  the  evolution  of  oxygen.  The  residue  consists  of  rubid- 
ium iodide. 

Diacid  Rubidium  lodate,  RbI0^.2HIOz.  —  For  the  prepa- 
ration of  this  compound,  5  g.  of  RbIO8  were  dissolved  in 
50  c.  c.  of  water  with  the  aid  of  heat,  then  13  g.  of  iodine 
pentoxide  in  50  c.  c.  of  water  were  added,  the  mixture  boiled 
down  to  half  its  volume  and  allowed  to  cool.  The  body 
separates  as  a  heavy,  crystalline  powder.  It  is  difficultly 
soluble  in  cold  water.  When  dissolved  in  hot  water  and 


62  ON  SOME  ALKALINE  IODATES. 

the  solution  left  to  crystallize,  RbIO3  separates.  The  product 
obtained,  as  stated  above,  was  separated  from  the  mother-liquor 
by  filtering  on  the  pump,  washed  with  a  little  cold  water  and 
dried  at  100°. 


Found. 

3 


Rubidium   ....  13.93  14.13  13.96 

Iodine    .....  61.91  62.48  62.20 

Oxygen  .....  23.74  .  .  .  23.51 

Hydrogen  ....  0.42  .  .  .  0.33 

This  compound  does  not  lose  water  at  100°.  When  heated 
it  does  not  decrepitate,  but  melts,  gives  off  water,  then  iodine 
and  oxygen,  leaving  a  residue  of  rubidium  iodide.  The  com- 
pound was  also  obtained  by  adding  10  c.  c.  of  hydrochloric 
acid  sp.  gr.  1.1  to  5  g.  of  RbIO8  in  20  c.  c.  of  water.  The  mix- 
ture was  warmed  until  all  the  RbIO3  dissolved,  when  it  gave 
a  faint  yellow  solution  which  slowly  deepened  in  color.  On 
standing,  a  well-crystallized  product  of  the  compound  under 
consideration  was  obtained,  containing  14.13  per  cent  of  rubid- 
ium and  62.19  per  cent  of  iodine. 

The  addition  of  a  saturated  solution  of  rubidium  chloride  to 
syrupy  iodic  acid  produces  a  precipitate  which  dissolves  again 
in  the  excess  of  iodic  acid.  When  more  rubidium  chloride 
is  added,  the  whole  being  kept  over  a  lamp,  a  point  is  reached 
where  a  precipitate  begins  to  form  in  the  hot  solution.  This 
is  the  compound  in  question.  It  was  identified  by  a  rubidium 
and  an  iodine  determination.  This  gave  14.17  per  cent  of 
rubidium  and  61.83  per  cent  of  iodine. 

RbCl.HIOz.  —  This  salt  can  be  made  by  simply  allowing 
a  saturated  solution  of  RbCl.Cl3I  to  stand  for  some  hours, 
when  large  colorless  prisms  form,  attached  to  the  plates  of 
RbCl.Cl3I.  The  solution,  after  removing  the  crystals,  warm- 
ing to  dissolve  the  pentahalide  and  passing  chlorine  in 
again,  does  not  yield  a  further  deposit  of  the  substance.  This 
is  explained  by  the  fact  that  so  much  hydrochloric  acid  is 
formed  in  the  solution  that  the  formation  of  this  compound  is 
prevented.  The  crystals  remain  unaltered  on  exposure  to  the 


ON  SOME  ALKALINE  IODATES.  63 

air,  but  on  treatment  with  cold  water  they  are  decomposed, 
losing  their  lustre  and  becoming  white.  The  solution  has  an 
acid  reaction  towards  litmus.  The  hot  saturated  solution  of 
this  compound  gives  the  normal  iodate  on  cooling.  The 
material  for  analysis  was  mechanically  separated  from  adher- 
ing RbCl.Cl3I  and  dried  in  the  air. 

Vn      ,  Calculated  for 

Found-  EbCl.HI03. 

Kubidium    .     .     .     28.88  .  .  .  28.78 

Iodine      ....     42.29  42.62  42.76 

Chlorine  ....     12.09  12.13  11.95 

Oxygen    ....     16.33  .  .  .  16.16 

Hydrogen 0.26  0.33 

This  salt  can  also  be  prepared  by  adding  a  strong  aqueous 
solution  of  rubidium  hydrate  to  a  strong  solution  of  iodine 
trichloride  in  water.  This  gives  at  first  a  precipitate  of  the 
compound  3RbC1.2HIO3,  and  the  solution  left  at  rest  for  a 
few  days  gives  the  large  well-developed  crystals  of  RbCl. 
HIO3  unmixed  with  RbCl.Cl8I.  These  were  identified  by 
their  crystalline  form. 

On  warming  the  crystals  with  hydrochloric  acid,  RbCl.Cl3I 
is  formed,  probably  according  to  the  following  equation : 

RbCl.HIOs  +  5HC1  =  RbCLClJ  +  3H20  +  Cl, 

and  the  RbCl.Cl3I,  on  further  heating,  gives  RbCl.ClI  with 
the  liberation  of  chlorine.  When  the  substance  is  heated  it 
melts,  gives  off  water,  chloride  of  iodine,  and  oxygen;  the 
residue  consists  of  rubidium  chloride  and  iodide.  A  deter- 
mination of  the  halogens  in  this  residue  gave  3.52  per  cent 
of  chlorine  and  53.66  per  cent  of  iodine. 

3Kb  01. 2HIO*.  —  This  compound,  which  is  analogous  to  the 
sodium  compound  3NaC1.2NaIO3.9H8O,  described  by  Ram- 
melsberg,*  and  also  to  the  salt  3NaI.2NaIO8.19H2O,  obtained 
by  Penny,  f  or  3NaI.2NaIO8.20H2O  according  to  Marignac,t 
except  that  it  contains  no  water  of  crystallization,  was  pre- 

*  Pogg.  Ann.,  xli,  648 ;  cxv,  584.  t  Ann.  Ch.  Pharm.,  xxxvii,  202. 

t  Jabresb.,  1857, 124 :  Ann.  Min.,  V,  ix,  1. 


64  ON  SOME  ALKALINE  IODATES. 

pared  by  two  methods.  It  was  obtained  by  the  addition  of  a 
hot,  strong,  aqueous  solution  of  rubidium  hydroxide  to  a 
strong  solution  of  iodine  trichloride,  the  latter  being  in  excess. 
The  mixture  was  then  filtered  hot,  and  on  cooling,  a  mass  of 
fine  needles  separated.  The  mother-liquor,  on  standing,  yielded 
the  large  crystals  of  RbCl.HIO3.  The  needles  are  stable  in 
the  air  and  at  100°.  From  the  hot,  saturated,  aqueous  solution 
of  the  compound,  the  normal  iodate  separates  on  cooling. 

The  formation  of  this  compound  was  also  observed  on 
adding  a  strong  solution  of  rubidium  carbonate  to  a  hot, 
saturated  solution  of  RbCl.ClsI,  the  latter  being  in  excess. 
The  colorless,  slender,  transparent  needles,  thus  obtained,  gener- 
ally separate  in  groups  radiating  from  a  point  on  the  surface 
of  the  yellow  crystals  of  RbCl.ClsI.  After  separating  the 
colorless  crystals  mechanically  from  the  pentahalide,  they 
were  air-dried  on  paper  and  then  analyzed,  while  the  material 
obtained  according  to  the  previous  method  was  dried  at 
100°. 

From  RbOH  Prom  Rb,CO3  Calculated  for 

and  IC13.  and  RbCl.Cl3I  3RbC1.2HIO3. 


Rubidium,  35.41  34.58  35.78  .  .  .  35.87 

Iodine,  35.27  36.00  35.87  35.81  35.52 

Chlorine,  14.99  14.82  15.26  15.16  14.90 

Oxygen,  .  .  .  13.15  .  .  .  13.64  13.43 

Hydrogen,  .  .  .  0.29  .  .  .  0.30  0.28 

When  heated,  the  substance  does  not  decrepitate,  but  melts, 
gives  off  chloride  of  iodine,  and  the  residue  consists  of  a 
mixture  of  rubidium  chloride  and  iodide.  A  sample  of  this 
residue  gave  on  analysis  9.68  per  cent  of  chlorine  and  38.91 
per  cent  of  iodine. 

Normal  Caesium  lodate,  OsIOs-  —  This  was  prepared  by  add- 
ing a  moderately  strong  aqueous  solution  of  iodic  acid  to  a 
strong  solution  of  caesium  carbonate,  care  being  taken  to  have 
the  carbonate  in  excess.  When  all  the  iodic  acid  had  been 
added,  the  solution  was  boiled.  On  cooling,  a  crystalline 
mass  separated,  consisting  apparently  of  small  cubes.  At  24°, 
100  parts  water  dissolve  2.6  parts  of  the  salt.  It  is  insoluble 


ON  SOME  ALKALINE  IODATES.  65 

in  alcohol.  The  body  was  prepared  for  analysis  by  filtering 
on  the  pump,  washing  with  cold  water,  and  then  pressing  on 
paper  and  drying  .at  100°. 

Analysis  gave  Calculated  for  CsIO3. 

Caesium       ....    43.08        43.53  43.18 

Iodine 40.84         .  .  .  41.23 

Oxygen 15.74         .  .  .  15.59 

This  was  also  obtained,  in  attempts  to  prepare  a  ceesium  salt 
corresponding  to  3RbC1.2HIO3,  by  adding  caesium  hydrate  or 
carbonate,  in  moderately  strong  aqueous  solution,  to  a  strong 
solution  of  iodine  trichloride  in  excess,  when  it  at  once  sepa- 
rated in  the  form  of  a  white  sandy  precipitate,  which  under 
the  microscope  was  seen  to  consist  of  transparent  grains  of 
indefinite  form.  Unless  the  iodine  trichloride  is  nearly  satu- 
rated with  the  carbonate,  CsCl.Cl8I  or  CsCl.ClI  *  is  obtained, 
mixed  with  the  iodate.  An  iodine  and  oxygen  determination 
in  the  air-dried  salt  gave  40.55  and  40.83  per  cent  of  iodine 
and  15.67  per  cent  of  oxygen.  When  this  iodate  is  heated,  it 
does  not  give  off  iodine,  but  melts  and  evolves  oxygen.  The 
residue  is  caesium  iodide. 

@CsIOs.I205.  —  This  substance  can  be  prepared  in  pure 
condition  and  in  large  quantity  by  mixing  a  moderately  dilute, 
aqueous  solution  of  two  molecules  of  caesium  chloride  with 
one  molecule  of  iodine  pentoxide  dissolved  in  a  little  water. 
Any  precipitate  that  may  have  been  produced  is  dissolved  by 
the  aid  of  heat  and  more  water  if  necessary.  On  cooling,  the 
compound  separates  as  a  sandy  powder.  This  can  be  washed 
with  water  or  recrystallized  from  hot  water  without  decompo- 
sition. It  can  also  be  recrystallized  from  dilute  solutions  of 
iodic  acid.  At  21°,  100  parts  of  water  dissolve  2.5  parts  of 
this  salt.  It  is  insoluble  in  alcohol.  The  material  for  analy- 
sis was  air-dried  after  pressing  on  paper. 

™       ,  Calculated  for 

Found.  2CsI08.I208. 

Caesium 27.93  28.00 

Iodine 53.42  53.47 

Oxygen 18.69  18.53 

*  Amer.  Jour.  Sci.,  HI,  xliii,  17,  and  xliv,  42. 
5 


66  ON  SOME  ALKALINE  IODATES. 

This  compound  invariably  separates  along  with  the  crystals 
of  CsCl.Cl8I,  when  the  latter  is  prepared  in  the  absence  of 
hydrochloric  acid,  but  the  yield  is  not  very  large.  It  is  thus 
obtained  in  the  form  of  small,  rounded,  white  nodules,  which, 
on  close  inspection,  are  seen  to  occur  in  pairs,  the  two  nodules 
being  on  opposite  sides  of  a  thin  layer  of  the  pentahalide. 
They  were  mechanically  separated  from  the  latter,  no  water 
being  used  to  wash  the  compound  when  prepared  for  analysis. 
The  f ollowing  results  are  sufficient  for  its  identification : 

Caesium 29.11 

Iodine 50.21 

Oxygen 18.99 

Chlorine 3.24 

This  compound  was  also  obtained  by  the  following  methods. 
By  mixing  6  g.  of  CsIO8,  20  c.  c.  of  water,  and  10  c.  c.  of 
HC1,  sp.  gr.  1.1.  When  the  mixture  was  boiled,  it  became 
yellow  and  chlorine  was  evolved,  and  when  cooled  the  sub- 
stance separated  as  a  crystalline  crust.  It  was  identified  by 
a  determination  of  caesium  which  gave  28.40  per  cent. 

The  compounds  2CsIO3.l2O5.2HIO3  and  CsCl.HIO3  give 
this  body  when  their  hot  saturated  solutions  are  cooled.  A 
caesium  determination  in  the  products  thus  obtained  gave 
27.94  and  28.12  per  cent  respectively. 

When  this  body  is  treated  with  hydrochloric  acid,  sp.  gr. 
1.1,  the  solution  becomes  yellow,  evolves  chlorine  on  warming, 
and,  when  concentrated  on  the  water  bath,  yields  on  cooling 
well-crystallized  CsCl.ClI.  Analysis  gave  50.68  per  cent  of 
caesium  chloride.  (Calculated  for  CsCl.ClI,  50.90  per  cent.) 

When  heated  in  a  closed  tube  it  gives  no  sign  of  water, 
gives  off  iodine,  then  melts  with  the  evolution  of  iodine  and 
oxygen.  The  residue  consists  of  caesium  iodide. 

2CsIOs.I2Os.gITIOs.—This  body  was  obtained  by  adding 
5  g.  of  2CsIO8.I2O6  to  a  boiling  solution  of  25  g.  of  iodine 
pentoxide  in  sufficient  water  to  form  a  syrup.  Water  was 
then  added,  and  the  precipitate  thus  produced  proved  to  be 
the  compound  in  question.  Thus  produced,  it  separates  as 


ON  SOME  ALKALINE  IODATES.  67 

a  finely  divided  amorphous  precipitate,  which  can  be  dried  in 
the  air  or  at  100°  without  losing  water.  It  is  difficultly  solu- 
ble in  water  and  when  crystallized  from  an  aqueous  solution 
gives  2CsIO3.I2O6.  An  analysis  of  the  substance  dried  at 
100°  gave: 

u^mH  Calculated  for 

2CsI03.I206.2HI08. 

Caesium       .....  19.71  20.43 

Iodine    ......  57.68  58.52 

Oxygen  ......  20.41  20.89 

Hydrogen  .....  0.12  0.16 

Water  determinations,  in  samples  dried  in  the  air  on  paper, 
gave  1.45  and  1.38  per  cent  ;  theory  requires  1.44. 

When  the  substance  is  heated  it  gives  off  water  and  iodine, 
then  oxygen,  the  residue  consisting  of  caesium  iodide. 

Cs  Cl.HIOy  —  This  was  obtained,  in  an  attempt  to  increase 
the  yield  of  2CsIO3.I2O5,  by  adding  a  rather  small  quantity  of 
caesium  carbonate  to  a  hot,  saturated  solution  of  CsCl.Cl3I, 
when,  on  cooling  and  allowing  the  mixture  to  stand,  colorless, 
flat,  transparent  prisms  separated  on  the  yellow  crystals  of 
CsCl.Cl3I  previously  formed.  These  colorless  prisms  were 
picked  out  from  the  solution,  dried  on  paper  and  separated 
mechanically,  as  far  as  possible,  from  any  adhering  CsCl.Cl8I. 
These  on  analysis  gave  the  following  results  : 


Calculated  for 
CsCLHIO,. 

Caesium  .....  38.09  .  .  .  38.60 

Iodine    .....  36.08  36.29  36.86 

Chlorine     ....  11.69  11.82  10.31 

Oxygen       ....  13.85  .  .  .  13.94 

Hydrogen   ....  0.30  .  .  .  0.29 

The  crystals  remain  unaltered  on  exposure  to  dry  air,  but 
on  treating  them  with  water  they  immediately  become  opaque. 
On  recrystallizing  from  water  they  give  2CsIO8.l2O6.  When 
the  substance  is  heated,  it  gives  off  water  and  iodine  chloride, 
melts,  and  gives  off  oxygen,  the  residue  consisting  of  chloride 
and  iodide  of  caesium.  When  it  is  warmed  with  hydrochloric 


68  ON  SOME  ALKALINE  IODATES. 

acid,  it  undergoes  the  same  decomposition  as  the  corresponding 
rubidium  compound. 

KOl.KIOz.HIOs.  —  This  compound  has  previously  been 
prepared  by  treating  KIO3  with  hydrochloric  acid,  or  a  solution 
of  iodine  trichloride  with  potassium  hydrate  or  carbonate.  It 
has  been  described  by  Serullas  *  and  Rammelsberg  f  as  anhy- 
drous, and  the  formula  2KC1.2KIO3.I2O5  was  assigned  to  the 
salt.  Millon,J  from  his  determination  of  potash  in  this  salt, 
concluded  that  the  substance  contained  a  molecule  of  water, 
but  he  made  no  determination  of  it.  Finally  Marignac,§  who 
examined  it  more  carefully,  made  a  determination  of  the  water 
by  drying  the  substance  at  100°,  then  igniting  it  in  a  tube 
with  metallic  copper  and  collecting  and  weighing  the  water 
by  means  of  a  sulphuric  acid  tube. 

The  compound  obtained  from  a  solution  of  KC1.C13I  sepa- 
rated in  shining  transparent  prisms,  stable  in  the  air.  It  con- 
tained water  corresponding  to  the  formula  2KC1.2KIO3.I2O6. 
H2O  or  KC1.KIO3.HIO3.  An  analysis  of  the  air-dried  salt 
gave  the  following  results: 

-pni,_^  Calculated  for 

KC1.KI03.HI03. 

Potassium 16.94        16.83  16.82 

Iodine 54.46          .  .  .  54.66 

Chlorine 7.72             .  .  7.64 

Oxygen 20.66 

Hydrogen      .....       0.20          .  .  .  0.22 

This  compound  and  the  one  obtained  by  Marignac  are 
therefore  identical. 

On  ignition  it  gives  off  water,  iodine  chloride,  and  oxygen, 
the  residue  consisting  of  potassium  iodide  and  chloride.  An 
analysis  of  this  residue  gave  2.39  per  cent  chlorine  and  70.87 
per  cent  iodine. 

The  author  takes  occasion  here  to  express  his  obligations  to 
Professor  H.  L.  Wells  for  the  use  of  the  material  in  this  in- 

*  Ann.  Ch.  Phys.,  II,  xliii,  113.  t  Ibid.,  Ill,  ix,  407. 

t  Pogg.  Ann.,  xcvii. 

§  Jahresb.,  1856,  298.    Ann.  Min.,  V,  ix,  1. 


ON  SOME  ALKALINE  IODATES. 


69 


vestigation  and  for  valuable  suggestions;  also  to  Professor 
S.  L.  Penfield,  who  has  kindly  furnished  the  crystallographical 
descriptions. 

NOTES  ON  THE  CRYSTALLINE  FORM  OF  RbCl.HIO8  AND 

CsCl.HIO8. 


The  form  of  RbCl.HIO3  is  monoclinic.  The 
crystals  are  highly  modified,  doubly  terminated 
prisms,  Fig.  1.  The  faces  gave  fair  reflections, 
and  the  measurements  which  were  chosen  as 
fundamental  are  marked  by  an  asterisk  in  the 
table  of  angles. 

The  axial  ratio  and  forms  are  as  follows  : 


a  :  3  :  b  =  0.9830  :  1  :  0.7577,     0  =  100  A  001  =  87°  56' 


a,  100,  i-l 

b,  010,  'i-i 

c,  001,  0 


I,  320,  i-I 
TO,  110,  I 
n,  120,  & 


d,  Oil,  1-i 

e,  101,  -1-i 
/,  101,  1-i 


9,  102,  ft 
a,  211,  -2-2 
ft  HI,  -1 


q,  142,  -24 
s,  211,  2-2 
u,  111,  1. 


Measured. 

Calcu 

late. 

a  A 

c, 

100 

A  001 

=  *87°  56' 

a  A 

e, 

100 

A  101 

=  *51°   5' 

C  A 

d.OOl 

A  Oil 

=  *37°   8' 

a  A 

I, 

100 

A  320 

=    33°  13' 

33° 

13' 

a  A 

M, 

100 

A  110 

=   44°   7' 

44° 

29-1 

a  A 

», 

100 

A  120 

=    62°  42' 

63° 

1| 

a  A 

0, 

100 

A  211 

=   38°  19' 

38° 

28A 

a  A 

P> 

100 

A  111 

=    57°  13' 

57°  14' 

The  form 
the  one  crop 


2. 


ments  could 
mental  are: 


Measured.  Calculated. 

a  A  d,  100  A  Oil  =r  88°  29'  88°  21' 

a  A  s,  TOO  A  211  =  38°  32'  39°  47' 

a  A  «,  100  A  111  =  59°  57'  59°  38' 

e  A  p,  101  A  111  =  30°  28'  30°  31' 

/AM,  101  A  111 -31°  22^'  31°  24' 

p  A  g,  111  A  142  =  26°  36'  26°  30' 

c  A  g,  001  A  102  =  21°  17'  21°  20' 

c  A  /,  001  A  101  =  38°  26'  38°  23|' 

CsCLHIOs 

of  CsCl.HIOg  is  monoclinic.     The  crystals,  from 
which  was  examined,  were  about  5  mm.  in  length 
and  had  the  habit  shown  in  Fig.  2. 
They  were  attached  at  one  end,  and 
usually  grew  in  radiating  and  diver- 
gent groups.     The  faces  were  not  very 
perfect,  and  only  approximate  measure- 
be  made.     Those  which  were  chosen  as  funda- 


70  ON  SOME  ALKALINE  IODATES. 

TO  A  m,  110  AllO  =  90°  12'     7/1  A  p,  110  A  221  =  24°  37'     a  A  P,  100  A  221  =  49°  63 
The  axial  ratio  and  forms  are  as  follows : 

d  ~b  :  c  =  0.9965  :  1  :  0.7698  £  =  100  A  001  =  89°  53£' 

a,100,w  m,  110,1         d,403, -fi  s,403,  fi  p,  221, -2 

c,  001,0  n,  130,  i4      e,  203, -ft  «,  203,  fi  o,  263,  -2-3 

The  pyramids  p  and  o  were  frequently  wanting.  The 
orthodomes  d,  e,  s,  and  u  were  very  constant  in  their  develop- 
ment and  gave  to  the  crystals  an  orthorhombic  habit.  Owing 
to  the  curved  and  striated  character  of  the  faces,  the  symme- 
try could  not  be  satisfactorily  determined  by  measurement, 
but  the  optical  properties  showed  that  the  crystals  were  truly 
monoclinic.  In  polarized  light  the  tables  show  an  extinction 
parallel  to  the  ortho-axis,  and  in  convergent  light  one  of 
the  optical  axes  and  the  acute  bisectrix  can  be  seen  near 
the  limits  of  the  field.  The  plane  of  the  optical  axes  is  the 
clino-pinacoid. 

These  two  salts,  although  entirely  different  in  crystalline 
habit,  are  very  similar  in  their  axial  ratios. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
April,  1892. 


ON  A  METHOD  FOB  THE  QUANTITATIVE  DETER- 
MINATION OF  CESIUM,  AND  THE  PREPARATION 
OF  PURE  OESIUM  AND  RUBIDIUM  COMPOUNDS.* 

BY  H.  L.  WELLS. 

SINCE  no  method  has  heretofore  been  devised  for  the  accu- 
rate quantitative  determination  of  csesium  in  the  presence  of 
both  rubidium  and  potassium,  some  experiments  have  been 
made  in  order  to  test  the  availability  of  the  plumbic  chloride, 
described  in  a  recent  article,  f  for  this  purpose.  The  results 
have  not  been  as  accurate  as  could  be  desired,  but  the  method 
will  be  useful  until  a  better  one  is  found. 

The  solubility  of  Cs2PbCl6  in  a  hydrochloric  acid  solution 
(fuming  acid  diluted  with  water  1:1),  containing  twice  the 
theoretical  amount  of  lead  chloride  and  saturated  with  chlorine, 
was  determined  by  making  a  precipitation  of  about  1  g.  of 
Cs2PbCl6  under  these  conditions  in  350  c.  c.  and  determining  the 
csesium  in  the  nitrate.  The  whole  filtrate  gave  0.0119  g.  of 
Cs2SO4,  which  corresponds  to  a  solubility  of  0.000068  g.  of 
Cs2PbCl6  in  1  c.  c.  A  similar  experiment  in  which  concentrated 
hydrochloric  acid  was  used,  and  also  a  larger  excess  of  lead 
chloride,  gave  a  solubility  of  0.00049  g.  of  Cs2PbCl6  in  1  c.  c. 
It  has  been  shown  in  the  article  referred  to  that  the  solubility 
of  Rb2PbCl6  is  0.003  g.  in  1  c.  c.  under  similar  conditions. 

Some  actual  determinations  of  caesium  were  made  as  follows : 
Known  quantities  of  Cs2PbCl6  and  about  an  equal  weight  of 
PbCl2  were  dissolved  in  hot  HC1  (1:1).  Chlorine  was  passed 
into  the  solutions  until  they  became  cold,  and,  after  standing 
about  three  hours,  the  precipitates  were  collected  in  porcelain 
Gooch  crucibles  and  washed  with  hydrochloric  acid  containing 
chlorine.  The  precipitates  were  decomposed  with  hot  water, 

*  Amer.  Jour.  Sci.,  xlvi,  September,  1893.  t  Ibid.,  p.  180. 


72 


QUANTITATIVE  DETERMINATION 


and  the  csesium  in  the  resulting  solutions  was  determined  as 
sulphate.  In  one  case  a  comparatively  large  amount  of  potas- 
sium chloride  was  present.  The  details  are  as  follows : 


A 
B 
C 


taken. 

.1674 
.1592 
.1280 


KCl 
taken. 


0.5 


Volume 


Cs2S04 


Deficiency 


1HC1. 

found. 

as  Cs2SO 

c.  c. 

35 

.0856 

.0026 

35 

.0807 

.0031 

35 

.0638 

.0035 

These  results  indicate  greater  errors  than  were  expected  from 
the  previous  solubility  determinations.  It  is  suspected  that  a 
little  of  the  precipitate  was  dissolved  by  washing,  and  the  use 
of  hydrochloric  acid  containing  lead  chloride  as  well  as  chlo- 
rine would  probably  diminish  the  error.  The  last  experiment 
shows  that  the  presence  of  a  considerable  amount  of  potassium 
has  no  influence  upon  the  result. 

The  determination  of  csesium  by  this  method  can  be  simpli- 
fied by  weighing  the  precipitated  caesium-plumbic  chloride 
directly.  The  salt  is  perfectly  stable  at  100°.  The  following 
table  gives  the  details  of  a  number  of  determinations  made  in 
this  way.  The  precipitates  were  all  thoroughly  washed  with 
hydrochloric  acid  containing  chlorine  and  dried  on  an  asbestos 
filter  at  100°. 


taken. 


PbCl2 
taken. 


KCl 

taken. 


Volume 
HC1. 


Cs2PbC!6 
found. 


g- 

A 

0.2761 

0.25 

B 

0.0878 

1.0 

C 

0.1202 

1.0 

D 

0.7558 

0.1 

E 

0.2483 

0.1 

0.5 


c.c. 

* 

g- 

28  1  :  1 

0.2650 

0.0111 

52  1  :  1 

0.0833 

0.0035 

52  1  :  1 

0.1071 

0.0131 

28  cone. 

0.7369 

0.0189 

20    cone.      0.2359      0.0124 


The  results  show  considerable  losses  in  csesium,  which  appar- 
ently do  not  entirely  depend  upon  the  volume  in  which  the 
precipitation  is  made.  It  is  believed  that  the  losses  occur 
chiefly  in  washing,  for  large  quantities  usually  show  a  larger 
total  loss  than  small  ones. 


OF  CAESIUM.  73 

When  caesium  and  rubidium  are  together,  the  precipitation 
of  caesium  plumbic  chloride  is  accompanied  by  a  partial  pre- 
cipitation of  the  rubidium,  unless  the  quantity  of  the  latter  is 
small.  It  is  possible,  however,  to  make  an  indirect  determina- 
tion of  the  caesium  in  such  a  precipitate  by  weighing  it  and 
afterwards  determining  the  weight  of  the  caesium  and  rubidium 
sulphates.  Two  experiments  have  been  made  on  this  plan, 
where  not  only  rubidium,  but  also  potassium,  sodium,  and 
lithium  were  present. 

A  B 

g.  g. 

Cs2PbCl6  taken,  0.3561  0.1545 

Rb2PbCl6  taken,  0.2845  0.4101 

To  each  of  these  were  added  about  0.15  g.  each  of  potassium 
and  sodium  chlorides,  0.25  g.  of  lithium  carbonate,  and  0.1  g.  of 
lead  chloride.  The  substances  were  dissolved  by  boiling  with 
dilute  hydrochloric  acid,  about  an  equal  volume  of  concen- 
trated acid  was  added,  and  chlorine  was  passed  until  the 
solutions  became  cold. 

A  B 

c.  c.  c.  c. 

Volume  of  solution,  30  50 

After  standing  several  hours,  the  precipitates  were  collected 
on  asbestos  filters  in  porcelain  Gooch  crucibles,  washed  with 
dilute  hydrochloric  acid  saturated  with  chlorine,  dried  at  100° 
and  weighed. 

A  B 

Cs2PbCl6  and  Eb2PbCl6  found,         0.5621        0.4538 

The  precipitates  were  treated  on  the  filters  with  hot  water, 
the  resulting  solutions  were  evaporated  with  sulphuric  acid, 
the  lead  sulphate  was  removed  by  filtration,  the  filtrates  were 
evaporated  and  finally  ignited  in  an  ammoniacal  atmosphere, 
and  the  mixed  sulphates  were  weighed. 

A  B 

Cs2S04  and  Eb2S04  found,          0.2826         0.2164 
For  calculating  the  results,  the  following  formulae  were  used: 


74  QUANTITATIVE  DETERMINATION 

(P  =  weight  of  Cs,PbCl6  +  Eb2PbCl6) 
(S  =  weight  of  Cs2S04  +  Kb2S04) 
Weight  of  Cs  =  5.095S  -  2.301P 
Weight  of  Eb  =  2.006P  -  3.801S 

A  B 

Caesium  taken 0.1381  0.0599 

Caesium  found 0.1464  0.0584 

Error  in  caesium 0.0083+  0.0015— 

Eubidium  taken 0.0823  0.1186 

Eubidium  precipitated    .  .     0.0534  0.0876 

The  results  show  that  approximate  determinations  of  caesium 
can  be  made  by  this  method  when  all  the  alkali-metals  are 
present.  The  process  leaves  a  part  of  the  rubidium  with  the 
potassium,  and  these  two  metals  can  be  precipitated  as  platinic 
chlorides  and  their  amounts  determined  indirectly. 

The  method  which  has  been  described  is  useful  for  the  ex- 
traction of  caesium  and  rubidium  from  their  natural  sources. 
The  following  method  of  procedure  may  be  suggested,  sup- 
posing all  the  alkali-metals  to  be  present  as  chlorides  in  a 
concentrated  aqueous  solution: 

At  least  an  equal  volume  of  concentrated  hydrochloric  acid 
is  added,  and  any  precipitated  sodium  and  potassium  chlorides 
are  removed.  The  solution  is  diluted  somewhat,  to  avoid  a 
subsequent  precipitation  of  these  chlorides,  a  solution  of  lead 
chloride,  made  by  boiling  lead  oxide  with  a  large  excess  of 
hydrochloric  acid,  is  gradually  added,  while  chlorine  is  passed 
into  the  solution  until  it  is  cold  and  until  fresh  additions  of 
lead  chloride  fail  to  produce  a  yellow  precipitate.  According 
to  my  solubility  determinations,  this  precipitation  leaves  less 
than  1  g.  of  rubidium  and  a  much  smaller  quantity  of  caesium  in 
each  liter  of  the  solution.  The  precipitate  is  usually  almost 
free  from  potassium.  To  ensure  the  complete  purification  of 
the  caesium  and  rubidium,  the  precipitate  is  washed  with 
hydrochloric  acid  containing  chlorine  and  lead  chloride,  then 
it  is  treated  repeatedly  with  small  quantities  of  boiling  water 
until  completely  decomposed,  and  the  resulting  solution  is 


OF  CAESIUM.  75 

subjected  to  a  repetition  of  the  foregoing  process.  The  mixed 
plumbic  salts  are  decomposed  with  hot  water,  and  the  resulting 
filtered  solution  is  evaporated  to  dryness  to  remove  hydrochloric 
acid.  The  residue  is  dissolved  in  hot  water,*  the  lead  is  precip- 
itated by  the  addition  of  a  slight  excess  of  ammonium  sulphide, 
and  the  precipitate  is  removed  by  filtration.  The  solution  is 
evaporated  to  dryness,  and  the  residue  consists  of  caesium  and 
rubidium  chlorides  and  some  ammonium  chloride. 

The  following  directions  for  the  separation  and  purification 
of  the  caesium  and  rubidium  do  not  involve  any  new  methods, 
but  the  course  of  procedure  has  been  arrived  at  after  a  consid- 
erable amount  of  experience,  and  it  may  be  of  use  to  others. 
It  is  assumed  that  rubidium  is  more  abundant  than  caesium 
in  the  mixture.  If  caesium  predominated,  it  would  be  more 
advantageous  to  extract  that  metal  first  by  an  obvious  modi- 
fication of  the  process. 

The  mixed  chlorides  of  rubidium  and  caesium  are  dissolved 
in  at  least  five  parts  of  concentrated  nitric  acid,  and  the  solution 
is  evaporated  to  dryness  and  heated  until  the  excess  of  nitric 
acid  is  removed.  The  residue  is  dissolved  in  a  small  amount 
of  water,  and  as  much  oxalic  acid  as  corresponds  to  twice  the 
weight  of  the  original  chlorides  is  added.  The  whole  is  evap- 
orated to  dryness,  and  the  residue  is  ignited  in  platinum  until 
the  oxalates  are  completely  converted  into  carbonates. f  The 
carbonates  are  dissolved  in  water,  the  solution  is  filtered  and 
exactly  neutralized  with  a  measured  solution  of  tartaric  acid, 
as  much  more  tartaric  acid  as  has  been  used  for  the  neutraliza- 
tion is  added,  and  the  solution  is  evaporated  until  it  becomes 
saturated  while  hot.  The  solution  on  cooling  deposits  acid 
rubidium  tartrate,  which  is  washed  with  a  small  quantity 
of  water  and  is  recrystallized  two  or  three  times  from  a  hot 
saturated  solution,  in  the  same  way,  until  it  gives  no  caesium 

*  No  part  of  this  residue  should  be  thrown  away  on  the  assumption  that  it 
is  lead  chloride,  for  the  salt  CsPb2Cl6  is  difficultly  soluble  and  resembles 
PbCl2. 

t  This  method  of  converting  alkaline  chlorides  into  carbonates  is  due  to 
J.  L.  Smith,  Amer.  Jour.  ScL,  II,  xvi,  373. 


76  DETERMINATION  OF  CESIUM. 

spectrum.*  The  united  mother-liquors  from  the  acid  rubidium 
tartrate  are  evaporated  to  dryness  and  ignited  in  platinum. 
The  resulting  carbonates  are  converted  into  chlorides,  and,  to 
a  solution  of  these  in  a  small  volume  of  1  :  1  hydrochloric 
acid,  a  solution  of  antimony  trichloride  in  the  same  acid  is 
added  as  long  as  a  precipitate  forms,  f  The  precipitate  is 
collected  on  a  filter  and  washed  with  hydrochloric  acid.  To  re- 
move traces  of  rubidium,  the  precipitate  is  thoroughly  decom- 
posed with  successive,  small  quantities  of  hot  water,  then 
hydrochloric  acid  and  a  little  antimony  trichloride  are  added 
to  the  whole,  in  order  to  repeat  the  precipitation.  The  last 
precipitate  is  washed  with  hydrochloric  acid.  It  usually  shows 
no  rubidium  when  tested  with  the  spectroscope.  The  caesium 
antimony  chloride  is  decomposed  with  hot  water,  and  hydrogen 
sulphide  is  passed  into  the  resulting  solution.  The  nitrate 
from  the  antimony  sulphide  gives,  on  evaporation,  pure  caesium 
chloride.  The  filtrates  from  the  antimony  double  salt  are 
freed  from  antimony,  evaporated  to  dryness,  and  the  mixture 
of  caesium  and  rubidium  chlorides,  which  should  be  very  small 
in  amount,  is  preserved  for  use  in  subsequent  purifications. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
April,  1893. 

*  This  method  is  due  to  O.  D.  Allen,  Amer.  Jour.  Sci.,  II,  xxxiv,  367. 
t  Method  of  Godeffroy,  Berichte,  vii,  375. 


ON    SOME   PECULIAR    HALIDES    OF    POTASSIUM 
AND  LEAD  * 

BY  H.  L.  WELLS. 

IN  a  recent  article  I  have  described  a  series  of  double  chlo- 
rides of  the  type  M2PbCl6,  where  M  is  NH4,  K,  Rb  and  Cs.  It 
has  seemed  desirable  to  extend  the  investigation  by  attempt- 
ing to  prepare  bromides  and  iodides  corresponding  to  these 
salts.  A  thorough  search  has  been  made,  using  the  metals 
of  the  potassium  group  and  sodium,  with  the  result  that  no 
double  bromides  or  iodides  containing  extra  halogen  could  be 
prepared,  except  in  the  case  of  potassium.  It  is  remarkable 
that  the  potassium-lead  bromide  and  iodide  which  have  been 
discovered  do  not  correspond  in  composition  to  the  chlorides. 
The  failure  to  prepare  double  salts  of  rubidium  and  caesium 
corresponding  to  the  new  potassium  compounds  was  unex- 
pected, for,  as  a  general  rule,  the  insolubility  and  stability  and 
the  consequent  ease  of  preparation  of  such  compounds  become 
greater  from  potassium  towards  caesium.  The  explanation  of 
the  anomaly  probably  lies  in  the  fact  that  extremely  concen- 
trated rubidium  and  caesium  solutions  containing  a  lead  halide 
and  the  corresponding  halogen  cannot  be  obtained,  in  the  case 
of  the  bromides  and  iodides,  on  account  of  the  slight  solubil- 
ity of  caesium  triiodide,  and  of  the  double  halides  which  are 
formed  with  PbBr2  and  PbI2. 

The  compounds  to  be  described  probably,  have  the  composi- 
tion represented  by  the  following  formulae : 

K8Pb2I8.4H20 
K8Pb2Br8.4H2O 

*  Amer.  Jour.  Sci.,  xlvi,  September,  1893. 


78  SOME  PECULIAR  HALIDES  OF 

These  formulae  may  be  also  written, 

3KI.2PbI2.I.4H2O  and  3KBr.2PbBr8.Br.4H20 

The  composition  of  these  salts  is  very  remarkable,  on  account 
of  the  small  amount  of  the  extra  halogen  that  they  contain. 
They  apparently  do  not  correspond  to  any  other  chemical  com- 
pound that  is  known. 

The  Iodide,  KsPb2 I^H^  0.  —  This  salt  forms  brilliant, 
black,  prismatic  crystals,  sometimes  a  centimeter  or  two  in 
length  and  three  or  four  millimeters  in  diameter.  Although 
the  crystals  have  fine  prismatic  faces,  they  never  appear  to 
have  definite  terminations.  The  ends  usually  appear  fibrous, 
as  though  made  up  of  numerous  small  crystals  in  parallel  posi- 
tion. When  the  crystals  are  crushed  on  paper  it  is  evident 
that  they  enclose  much  mother-liquor.  The  salt  is  deposited 
from  nearly,  or  quite,  saturated  solutions  of  potassium  iodide 
containing  lead  iodide  and  iodine.  It  is  deposited  at  ordinary 
temperature,  usually  slowly,  after  the  lapse  of  several  hours  or 
even  after  several  days.  In  preparing  the  compound,  the  lead 
iodide  and  the  iodine  can  be  varied  considerably,  but  it  is 
formed  only  in  very  concentrated  potassium  iodide  solutions, 
and  it  is  difficult  to  obtain  crops  of  it  which  are  not  evidently 
contaminated  with  this  salt  in  the  form  of  crystals.  The  salt 
is  stable  in  the  air,  but  it  is  instantly  decomposed  by  water  or 
alcohol,  so  that  it  cannot  be  washed. 

Six  separate  crops  have  been  analyzed,  and  great  care  has 
been  used  in  selecting  them  and  in  drying  -them  on  paper  for 
analysis.  In  two  cases  the  product  was  rapidly  and  finely 
pulverized  during  the  drying  operation,  but  without  any  effect 
upon  its  composition.  The  results  of  the  six  analyses  agree 
with  remarkable  closeness,  but  in  spite  of  this  fact  it  must  be 
assumed,  from  considerations  which  will  be  given  subsequently, 
that  all  these  products  were  seriously  contaminated  with  potas- 
sium iodide.  The  fibrous  nature  of  the  crystals,  and  the  con- 
centration of  the  mother-liquor,  make  the  possibility  of  such  a 
contamination  very  evident,  but  the  constancy  of  this  contam- 
ination, as  indicated  by  the  uniformity  of  the  analyses,  is  very 


POTASSIUM  AND  LEAD.  79 

remarkable  in  view  of  the  fact  that  some  of  the  products  were 
made  at  wide  intervals  of  time,  covering  a  period  of  about  six 
months,  so  that  there  were  considerable  variations  in  the 
laboratory  temperature. 

The  products  were  made  under  the  following  conditions  : 

KI.  Phi*  I.  Volume, 

g.  g.  g.  c.c. 

A  ...  450  30  15       ? 

B  ...  425  30  50  450 

C  ...  445  40  70  470 

D  ...  445  40  100  470 

E  ...  445  40  150  460 

F  ...  200  15  15  200 

They  gave  the  following  results  on  analysis : 

A  .  . 

B  .  . 

C  .  . 

D  .  . 

E  .  . 

F  .  . 

In  these  analyses,  and  those  which  follow,  water  was  deter- 
mined by  weighing  it  directly  in  a  calcium-chloride  tube. 
The  other  determinations  were  made  according  to  the  methods 
mentioned  in  the  preceding  article  on  the  double  salts  of  lead 
tetrachloride. 

The  above  analyses  correspond  closely  to  the  formula 
K9PbJi9.10H2O,  but  it  will  be  shown  beyond  that  the  proba- 
ble formula  of  the  pure  compound  is  K8Pb2l8.4H4O.  This 
requires  K  =  7.25,  Pb  -  25.56,  I  -  62.74,  and  H2O  =  4.45.  If 
this  is  the  true  composition,  it  must  be  assumed  that  all  of  the 
analyzed  products  were  contaminated  with  about  16.5  per  cent 
of  potassium  iodide,  and  that  an  excess  of  water  was  present, 
possibly  on  account  of  the  hygroscopic  properties  of  that  salt. 

It  is  to  be  noticed  that  the  products  were  prepared  under 
great  variations  in  the  amount  of  iodine  present,  and  it  can 
be  safely  assumed,  from  the  care  with  which  the  products 


K. 

Pb. 

i. 

H20. 

9.31 

22.03 

64.00 

4.69  = 

100.03 

9.25 

22.30 

.  .  . 

4.81 

.  .  . 

9.07 

22.03 

63.98 

4.89  = 

99.97 

9.21 

21.98 

64.09 

4.71  = 

99.99 

9.20 

22.13 

64.17 

9.27 

22.02 

63.84 

80  SOME  PECULIAR  HALIDES   OF 

were  examined,  that  they  were  not  contaminated  with  the  salt 
KPbI3.2H2O  nor  any  similar  compound.  The  amount  of  lead 
iodide  in  the  solutions  was  comparatively  small,  and  a  large 
part  of  it  was  used  in  forming  the  salt  under  consideration,  so 
that  any  contamination  must  have  been  chiefly  potassium  iodide. 
It  is  therefore  evident,  since  the  salt  is  not  decomposed  on 
exposure,  and  since  the  analyses  show  a  constant  amount  of 
extra  iodine  in  spite  of  the  variations  of  this  ingredient  in  the 
solutions,  that  the  analyses  must  show  the  true  ratio  between 
the  lead  iodide  and  the  extra  iodine  in  the  pure  compound. 
This  ratio  is  2PbI2 : 1  in  both  K9Pb  J19  and  K3Pb2I8. 

The  Bromide,  K^Pl2Br^Hz  0.  —  This  compound  forms 
dark  brown,  prismatic  crystals,  which  are  solid  and  definitely 
terminated,  so  that  they  do  not  have  the  tendency  to  hold 
inclosed  mother-liquor  which  the  iodide  has.  The  salt  is  easily 
prepared  and  it  crystallizes  well,  but  it  is  extremely  unstable. 
When  exposed  to  the  air,  it  begins  to  whiten  almost  instantly, 
giving  off  bromine.  It  is  stable,  however,  in  air  containing  a 
considerable  amount  of  bromine  vapor,  so  that  it  can  be  dried 
by  pressing  on  paper  in  such  an  atmosphere.  It  is  sufficiently 
stable,  when  corked  up  in  a  weighing-tube,  to  be  rapidly 
weighed  in  a  cold  room  without  serious  decomposition. 

Three  crops  of  the  double  bromide  were  analyzed.  A  and 
B  were  made,  in  each  case,  by  adding  20  c.  c.  of  bromine  to 
400  c.  c.  of  a  cold  solution  which  was  saturated  with  potas- 
sium bromide  and  lead  bromide,  and  allowing  the  mixture  to 
stand  over  night.  C  was  made  like  the  other  crops,  except 
that  30  c.  c.  of  bromine  were  used. 

Found.  Calculated  for 


Potassium  . 
Lead  . 

A. 

.    .    10.33 
.     .     32.05 

B. 

10.41 
31.90 

c. 

10.24 
32.49 

K3Pb2Br8.4H80. 

9.43 
33.30 

Bromine 
Water     .     . 

.     .    51.96 

52.15 
5.59 

52.05 
5.28 

51.48 
5.79 

100.05      100.06          100.00 


The  analyses  agree  with  the  formula  as  well  as  could  be 
expected,  considering  the  instability  of  the  compound.     The 


POTASSIUM  AND  LEAD. 


81 


analyses  show,  almost  exactly,  one  atom  of  extra  bromine  for 
two  atoms  of  lead,  so  that  the  compound  is  closely  related  to 
the  iodide,  if  not  exactly  analogous  to  it. 

The  satisfactory  crystals  of  the  bromide,  and  the  stability  of 
the  iodide,  suggested  the  possibility  that,  if  the  two  compounds 
were  really  analogous,  as  suspected,  isomorphous  mixtures  of 
the  two  could  be  made  which  would  retain  the  desirable  quali- 
ties of  both,  so  as  to  be  solidly  crystallized  and  stable  enough 
to  be  accurately  analyzed.  Experiments  showed  that  isomor- 
phous mixtures  could  be  readily  obtained  which  crystallized 
satisfactorily,  and  it  was  found  that  even  small  amounts  of 
iodine  had  the  effect  of  greatly  increasing  the  stability  of  the 
compound.  It  was  noticed  that  when  a  product  was  made 
from  a  solution  containing  free  bromine  and  iodine  in  nearly 
atomic  proportions  (BrI),  an  almost  perfectly  stable,  bright 
red  salt  was  obtained.  The  color  of  this  salt  is  far  from  being 
intermediate  between  that  of  the  black  iodide  and  the  dark 
brown  bromide,  but,  since  the  analyzed  products  contain 
about  23  atoms  of  bromine  to  one  of  iodine,  it  does  not  seem 
probable  that  any  definite  relation  between  the  two  halogens 
exists.  It  is  remarkable  that  such  a  small  proportion  of 
iodine  should  have  so  great  an  influence  upon  the  color  and 
stability  of  the  product,  but  it  is  to  be  noticed  that  only  one- 
eighth  of  the  halogens  in  these  compounds  is  in  excess,  so 
that,  if  all  the  iodine  is  in  this  condition,  it  amounts  to  about 
one-third  of  this  excess. 

The  crops  A  and  B  had  a  dark  bronze  color.  They  were 
successive  crops,  made  by  adding  bromine  to  a  strong  solution 
of  potassium  iodide  containing  lead  iodide.  The  exact  con- 
ditions are  unknown,  but  it  is  probable  that  insufficient 
bromine  was  used  to  set  free  all  the  iodine  which  the  solution 
contained.  These  products  were  apparently  as  stable  as  the 
iodide. 

C  and  D  were  successive  crops,  made  by  continuing  the  addi- 
tion of  bromine  to  a  somewhat  similar  solution  until  a  change 
of  color  showed  that  the  free  iodine  had  been  converted  into 
BrI.  These  salts  were  red.  An  analysis  of  the  mother-liquor 

6 


82  SOME  PECULIAR  HALIDES  OF 

from  D  gave,  KBr  =  31.3,  PbBr2  =  1.8,  Br  =  6.7,  I  =  8.3, 
HaO  (difference)  =  51.9. 

E  was  made  by  adding  31  g.  of  bromine  to  430  g.  of  the 
above-mentioned  analyzed  solution.  This  crop  was  also  red, 
but  it  was  not  quite  as  bright  in  color  and  not  as  stable  as 
the  others.  On  continuing  the  addition  of  bromine,  still  less 
stable  crops  were  obtained,  which  approached  the  pure  bromide 
in  color.  These  were  not  analyzed. 

The  analyses  of  the  five  crops  are  as  follows : 


A  . 
B  . 

K. 

.    .    9.41 
.     .     9.24 

Pb. 

31.57 
31.55 

Br. 
41.40 

39.27 

i. 
12.06 
14.57 

HaO. 

5.09  = 

99.53 

C  . 

D  . 

E  , 

.     .     9.90 
.    .     9.99 
.  10.24 

32.88 
32.74 
32.26 

48.66 
48.70 
49.97 

3.40 
3.30 
2.07 

5.24  = 
5.02  = 

100.08 
99.75 

The  ratios  calculated  from  the  above  analyses  are  as  follows  : 

K          :          Pb       :       Br  +  I        :        H20. 

A 1.57  1.  3.99  1.83 

B 1.55  1.  3.99 

C 1.59  1.  4.00  1.82 

D 1.61  1.  4.00  1.76 

E 1.68  1.  4.16 

The  ratio  required  for  the  formula  K3Pb2(Br,I)8.4H20  is 

K  :  Pb  :  Br  + 1  H,O. 

1.50  1.  4.  2. 

The  analyses  agree  well  with  this  formula,  except  that  the 
water  is  somewhat  low.  Although  3J  molecules  of  water 
would  correspond  more  closely  to  these  analyses  than  4,  the 
latter  number  is  considered  more  probable,  on  account  of  the 
fact  that  the  analyses  of  the  iodide  show  some  excess  over 
four  molecules. 

It  is  to  be  seen  that  these  mixed  salts  correspond  in  com- 
position to  the  bromide.  The  analogous  mode  of  formation 
of  the  iodide,  the  identical  relation  of  the  lead  to  the  extra 
halogen  in  the  iodide  and  the  other  products,  as  well  as  the 


POTASSIUM  AND  LEAD.  83 

existence  of  these  mixed  salts,  make  it  appear  certain  that 
the  analyzed  iodide  was  invariably  impure,  and  that  the  pure 
compound  should  be  considered  as  analogous  to  the  other 
salts.  This  view  has  been  confirmed  by  a  crystallographic 
examination  of  the  iodide  and  the  red  bromo-iodide,  which 
Prof.  S.  L.  Penfield  has  kindly  undertaken.  He  has  found 
that  both  these  salts  crystallize  in  prisms  of  the  tetragonal 
system.  Unfortunately  the  crystals  of  the  iodide  were  with- 
out terminations,  so  that  a  more  detailed  comparison  of  the 
two  salts  could  not  be  made. 

The  nature  of  these  peculiar  salts  is  not  clear.  If  they 
are,  strictly,  hydrous  "  double  salts,"  such  higher  halides  as 
Pb2Is  or  K8I4  must  be  assumed.  If  they  are  formed  from  such 
compounds  as  PbI4  or  KI8,  they  must  be  considered  as  hydrous 
triple  salts. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
April,  1893. 


ON    THALLIUM    TRIIODIDE  AND  ITS    RELATION 
TO   THE   ALKALI-METAL  TRIIODIDES.* 

BY  H.  L.   WELLS  AND  S.  L.   PENFIELD. 

THE  well-known  resemblance  between  the  thallous  salts  and 
many  of  the  corresponding  alkali-metal  salts  has  led  us 
to  prepare  thallium  triiodide  and  to  compare  its  crystalline 
form  with  that  of  the  alkali-metal  triiodides.f  As  a  result, 
it  has  been  found  that  T1I3  agrees,  with  remarkable  closeness, 
in  form  with  RbI3  and  CsI3,  and  thus  a  case  of  isomorphism 
is  established  between  the  higher  iodides  of  thallium  and  the 
alkali-metals. 

This  isomorphism  is  of  special  interest  because  our  study 
of  the  trihalogen  compounds  of  csesium  has  led  us  to  the  con- 
clusion that  these  have  the  structure  of  double  salts.  We 
consider  the  evidence  of  this  double-salt  structure  as  very 
strong,  and  since  it  seems  necessary  to  infer  that  isomorphism 
indicates  the  same  arrangement  of  the  atoms,  we  are  obliged, 
in  spite  of  the  apparent  trivalence  of  thallium  in  thallic  com- 
pounds, to  conclude  that  T1I3  is  also  a  double  salt,  to  which 
the  formula  T1I.I2  should  be  given.  It  is  not  safe  to  assert 
at  present  that  all  thallic  salts  must  be  similarly  constituted, 
for  it  is  possible  that  thallium  triiodide  is  not  a  true  thallic 
compound  at  all,  and  that  thallic  sulphate,  nitrate,  etc.,  have 
an  entirely  different  kind  of  structure.  If  it  is  granted  that 
thallium  triiodide  is  a  double  salt,  it  seems  probable  that  many 
other  compounds,  which  are  considered  as  showing  higher 
valence  of  elements,  may,  in  reality,  have  the  structure  of 
double  salts  or  "  addition  products." 

Thallium  triiodide  was  first  described  by  Nickles,J  who  pre- 
pared it  by  evaporating  an  ethereal  solution  of  thallous  iodide 

*  Amer.  Jour.  Sci.,  xlvii,  June,  1894. 

t  Ibid.,  in,  xliii,  17  and  475.  }  J.  Pharm.  [4],  1,  25. 


ON  THALLIUM  TRI IODIDE. 


85 


and  iodine.  Nickl£s  states  that  he  did  not  obtain  it  in  -a  pure 
condition,  but  that  his  product  always  contained  an  excess  of 
iodine.  He  described  its  crystalline  form,  and  his  results 
will  be  mentioned  beyond. 

We  have  modified  Nickles'  method  by  using  alcohol  as  a 
solvent,  and  have  encountered  no  difficulty  in  obtaining  a 
pure  product.  The  amount  of  iodine  used  was  slightly  in 
excess  of  the  calculated  quantity,  and  the  solution,  produced 
after  long  digestion,  was  evaporated  over  sulphuric  acid  until 
crystallization  took  place.  The  resulting  crystals  were  fre- 
quently of  large  size,  perfectly  black,  with  a  magnificent  lustre 
which  was  slowly  lost  upon  exposure.  A  sample  of  the  salt, 
simply  pressed  upon  paper,  gave  the  following  results  upon 
analysis : 

'alcula^d 

Thallium  .  34.22  34.87 


Iodine  . 


64.80 


65.13 


An  examination  of  the  crystals  has  shown  that  they  are 
orthorhombic  and  isomorphous  with  the  orthorhombic  alkali- 
metal  trihalides.  Moreover,  all  the  forms  which  have  been 
observed  have  also  been  found  on  the  alkali-metal  salts,  and 
are  as  follows : 


a,  100,  irl 

b,  010,  i-i 

1. 


c,  001,  o 

ff,  012, 


d,  Oil,  1-T       p,  111,  1 
?,  102,  \-l 

a. 


a 


The   habit  is   shown  in  Figs.  1   and   2,  the  latter  being 
remarkably  like  that  of  CsI8,  when  this  had  been  crystallized 


86  ON  THALLIUM  TRIIODIDE. 

from  alcohol.  The  measurements  which  were  chosen  as  funda- 
mental are  d  A  d,  Oil  A  Oil  =  96°  34'  and  e  A  e,  102  A  102  = 
78°  48',  giving  the  axial  ratio  : 

a:b:c  =  0.6828  :  1  :  1.1217 

The  dome  g  was  determined  by  the  measurement  g  A  #, 
012  A  012  =  58°  34',  calculated  58°  34',  and  the  pyramid  p  by 
its  position  in  the  zones  a  —  d  and  d  —  e. 

A  description  of  this  salt,  including  a  figure,  has  been  given 
by  Nickle"s.  His  salt,  crystallized  from  ether,  had  the  habit 
shown  in  Fig.  3,  the  letters  in  brackets  being  those  used  by 
him  and  the  position  being  changed  to  correspond  with  the 
orientation  of  the  alkali-metal  trihalides.  He  considered  p  as 
a  prism,  t  as  a  macropinacoid,  and  m  and  n  as  brachydomes. 
No  calculations  are  given,  and  only  the  following  four 
measurements : 

Nickles.          Measured.  Calculated  from  author's  measurement. 

p  A  p  =  100°  15'  101°  12'  for  e*e,  102  A  102 

p  A   t  =    39°  22'  39°  24'   "   e  A  c,  102  A  001 

p*m=    61°  59°    3'   «   «  A  rf,  102  A  Oil 

n*    t=    19°  25'  20°  30'   "              013  A  001 

The  agreement  between  the  measured  and  calculated  angles 
is  not  very  close,  but  Nickles'  measurements  cannot  be  very 
exact,  for  if  we  take  p  A  £  =  39°  22'  and  n  A  t=19°  25'  as 
fundamental,  we  find  by  calculation  ^>A^  =  101°16'  and 
p  A  m  =  57°  55',  which  vary  considerably  from  his  measure- 
ments. Nickles  crystals  differ  from  ours  not  only  in  habit  but 
in  having  the  one-third  brachydome  w,  013,  which  has  not 
been  observed  either  in  the  T1I3  prepared  from  alcohol  or  on 
any  of  the  alkali-metal  trihalides  prepared  by  us. 

The  very  close  agreement  between  the  forms  of  rubidium, 
caesium,  and  thallium  triiodides  is  to  be  seen  from  the  follow- 
ing table  of  axial  ratios  : 

RbI8  .  .  .  a:b:c  =  0.6858  :  1  :  1.1234 
CsI8  ...«««=  0.6824  :  1  :  1.1051 
T1I8  .  .  .  "  "  "  =  0.6828:1:1.1217 


ON   THALLIUM  TRI IODIDE.  87 

Our  previous  observation,  that  the  exchange  of  one  metal 
for  another  in  the  trihalogen  compounds  usually  has  little  or 
no  effect  upon  the  crystalline  form,  is  strongly  confirmed  by 
these  ratios,  and  the  remarkable  agreement  between  the  ru- 
bidium triiodide  and  the  thallium  compound  is  very  striking, 
when  the  great  difference  between  the  atomic  weights  of  the 
two  metals  is  considered. 

It  was  hoped  that  a  pentaiodide  of  thallium  could  be  pre- 
pared, in  order  that  its  form  might  be  compared  with  that  of 
caesium  pentaiodide,  but,  by  the  use  of  increasing  proportions 
of  iodine  with  thallium  triiodide  in  alcoholic  solutions,  no  evi- 
dence of  the  existence  of  such  a  compound  could  be  obtained. 

The  remarkably  close  relations  of  thallium  to  the  alkali- 
metals,  as  far  as  the  thallous  compounds  are  concerned,  and 
the  additional  resemblance  which  has  been  pointed  out  in  the 
present  communication,  have  led  us  to  consider  the  possibility 
that  thallium  has  been  wrongly  placed  in  the  periodic  system 
of  the  elements  and  that  it  really  belongs  to  the  alkali  -metals. 
There  are  two  vacancies  in  Mendele*eff's  table  in  the  alkali- 
metal  group  corresponding  to  atomic  weights  of  about  170  and 
220.  One  of  these  is  smaller,  the  other  larger  than  the 
accepted  atomic  weight  of  thallium,  so  that,  as  far  as  these 
numbers  are  concerned,  thallium  might  be  composed  of  two 
alkali-metal  elements.  Although  the  probability  that  thal- 
lium was  composed  of  two  elements  seemed  very  slight  from 
other  considerations,  we  have  deemed  it  desirable  to  test  the 
question  experimentally. 

About  200  g.  of  thallium  were  converted  into  the  nitrate, 
and  this  was  systematically  fractionated  by  crystallization, 
until  about  one-twentieth  of  the  salt  remained  as  a  repeatedly 
recrystallized  portion,  and  about  another  twentieth  was  con- 
tained in  a  final  mother-liquor.  From  each  of  these  two  frac- 
tions, thallous  chloride  was  prepared  by  converting  into 
sulphate,  precipitating  impurities  with  hydrogen  sulphide,  and 
finally  precipitating  thallous  chloride  by  means  of  hydrochloric 
acid.  The  preparations  were  carefully  washed,  dried  at  100°, 
and  the  chlorine  was  determined  as  silver  chloride  in  order  to 


88  ON   THALLIUM  TRIIODIDE. 

get  the  atomic  weight  of  the  metal  in  each  fraction.  The  silver 
chloride  was  weighed  hi  the  Gooch  crucible,  a  method  which 
can  be  most  highly  recommended  for  accurately  weighing  this 
substance.  The  following  results  were  obtained,  the  weights 
being  given  as  taken  in  air  : 

Crystallized  End.      Soluble  End. 
g-  g- 

T1C1  taken 3.9146          3.3415 

AgCl  obtained 2.8393          1.9968 

Atomic  weight  of  Tl  (0  =  16)  .       204.5  204.5 

It  was  not  expected  that  absolute  accuracy  in  the  atomic 
weight  of  thallium  would  be  attained,  but  since  the  same 
method  of  purification  and  analysis  was  used  in  both  cases,  the 
two  results  are  comparable  with  each  other,  and  their  exact 
agreement  shows  that  the  fractionation  of  the  nitrate  gives  no 
change  in  the  atomic  weight  of  thallium,  and  no  evidence  has 
been  obtained  that  thallium  is  not  homogeneous. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
January,  1894. 


ON  SOME  COMPOUNDS  CONTAINING  LEAD  AND 
EXTRA  IODINE.* 

BY  H.  L.  WELLS. 

ABOUT  two  years  ago,  the  writer  described  f  the  double  salts 
of  lead  tetrachloride,  (NH4)2PbCl6,  K2PbCl6,  Rb2PbCl6,  and 
Cs2PbCl«,  and  upon  attempting  to  prepare  the  corresponding 
bromides  and  iodides,  an  entirely  different  kind  of  double  salts 
was  discovered.:):  These  peculiar  salts  were  K8Pb2Br8.4H2O 
and  K3Pb2l8.4H2O.  They  are  remarkable  in  containing  but  a 
single  atom  of  extra  halogen  hi  the  formula  as  given  above, 
and  they  apparently  correspond  to  no  previously  known  com- 
pound. I  was  unable  to  obtain,  with  the  alkali  metals,  any 
bromides  or  iodides  corresponding  to  the  chlorides,  but  it  is 
interesting  to  notice  that  Classen  and  Zahorski  §  have  obtained 
such  salts  with  quinoline,  (C9H,NH)2Pb6Br6  and  (C9H7NH)2 
PbI6.|| 

The  isolation  of  lead  tetrachloride  by  Friedrich,^[  and  the 
discovery  of  lead  tetraacetate,  Pb(CH3CO2)4,  by  Hutchinson 
and  Pollard,**  were  very  interesting  additions  to  our  knowledge 
of  the  compounds  of  tetravalent  lead.  These  articles  appeared 
almost  simultaneously  with  that  of  Classen  and  Zahorski,  which 
has  been  referred  to  above,  and  with  my  own  work  mentioned 
at  the  beginning  of  this  article. 

As  a  sequence  to  my  former  investigations,  it  has  seemed 
to  be  desirable  to  reinvestigate  two  previously  described  com- 
pounds containing  lead  and  extra  iodine,  because  it  seemed 

*  Amer.  Jour.  Sci.,  1,  July,  1895. 

t  Ibid.,  xlvi,  180,  1893.    "  t  Ibid.,  190,  1893. 

§  Zeitschr.  fur  anorg.  Chem.,  iv,  107,  1893. 

||  Classen  and  Zahorski  gave  a  formula  of  different  type,  6NH4C1.2PbCl4, 
to  the  double  ammonium  chloride.  It  seems  certain  from  analogy,  from 
Friedrich's  results,  and  from  my  own  work,  that  their  product  was  contami- 
nated with  ammonium  chloride. 

IF  Berichte,  xxvi,  1434, 1893.  **  Chem.  Soc.  Jour.,  Ixiii,  1136,  1893. 


90  ON  SOME   COMPOUNDS   CONTAINING 

possible  that  a  further  study  of  them  might  throw  some  light 
upon  the  nature  of  the  curious  salt,  K3Pb2I8.4H2O. 

Johnson's  Salt.  —  By  mixing  a  hot,  concentrated  alcoholic 
solution  of  potassium  triiodide  with  a  saturated  solution  of 
lead  acetate  in  boiling  alcohol,  filtering  off  the  small  precipi- 
tate thus  produced,  and  cooling,  G.  S.  Johnson  *  obtained  a 
crystalline  substance  to  which  he  gave  the  formula,  Pb8C86H54 
O28K6Ii7.  Concerning  this  he  remarks,  "The  formation  of  a 
rational  formula  has  at  present  baffled  all  my  endeavors." 

Johnson  also  obtained  the  salt  by  recrystallization  from  alco- 
hol and  by  evaporating  the  mother-liquor  over  sulphuric  acid, 
but  there  is  no  evidence  that  he  analyzed  more  than  one  sam- 
ple of  it.  He  does  not  give  the  quantities  used  in  making  his 
preparation. 

I  have  made  a  large  number  of  crops  of  the  compound,  all 
of  which  agreed  with  Johnson's  description  in  forming  rectan- 
gular crystals,  of  a  black  color,  having  a  marked  brassy  lustre 
upon  four  of  the  six  faces,  and  occurring  usually  in  intergrown 
groups  of  nearly  square,  flat  plates.  In  preparing  these  prod- 
ucts the  conditions  were  varied  considerably.  As  a  starting- 
point  30  g.  of  potassium  iodide  and  50  g.  of  iodine  were 
invariably  used.  These  amounts  give  a  slight  excess  of  iodine 
over  the  proportion  required  for  potassium  triiodide.  From 
40  to  100  g.  of  crystallized  lead  acetate  were  used,  and  it  was 
found  that  beyond  these  limits  the  preparation  was  unsuccessful. 

The  solvent  varied  from  absolute  alcohol,  diluted  only  with 
the  water  of  crystallization  of  the  lead  acetate,  to  alcohol 
diluted  with  one-half  its  volume  of  water.  Several  crops  were 
prepared  in  the  presence  of  glacial  acetic  acid,  and  a  volume  of 
this  amounting  to  TV  of  the  total  liquid  (20  c.  c.)  was  used  with 
success.  The  total  volume  of  solvent  varied  from  200  to 
500  c.  c.,  the  larger  amounts  being  used  when  it  was  not  ex- 
pected to  obtain  the  product  by  simple  cooling.  It  was  custom- 
ary to  dissolve  the  potassium  iodide  and  iodine  in  about  one-half 
of  the  solvent  to  be  used  and  the  lead  acetate  in  the  remainder. 
The  solutions  were  sometimes  mixed  boiling  hot,  while  at 

*  Chem.  Soc.  Jour.,  xxxiii,  189, 1878. 


LEAD  AND  EXTRA   IODINE.  91 

other  times  a  lower  temperature  was  employed.  A  precipitate, 
evidently  consisting  chiefly  of  lead  iodide,  was  always  pro- 
duced by  mixing  the  two  liquids,  but  its  quantity  was  usually 
small.  The  effect  of  the  presence  of  iodine  in  preventing  the 
precipitation  of  lead  iodide  to  a  great  extent  is  very  remark- 
able. The  solutions  were  filtered,  sometimes  while  hot,  some- 
tunes  after  a  longer  or  shorter  period.  The  products  obtained 
by  cooling  formed  coherent  crusts  composed  of  very  small, 
intergrown  crystals,  while  by  evaporation  over  sulphuric  acid 
much  larger  isolated  crystals,  or  groups  of  crystals,  were 
deposited.  All  the  analyses  given  below  were  made  upon 
crops  obtained  by  evaporation,  except  in  one  instance.  Two 
partial  analyses  of  products  made  by  cooling  are  not  included 
in  the  list,  because  the  results  varied  rather  widely  from  each 
other  and  from  the  results  obtained  with  the  products  of  evapo- 
rations. The  omitted  results  differed  still  more  from  Johnson's 
analysis  than  the  others.  Two  or  three  successive  crops  were 
often  obtained  by  evaporating  a  single  solution,  and  the  twelve 
products,  analyses  of  which  are  given,  represent  six  different 
original  solutions.  The  products  were  well  crystallized  and 
most  of  them  seemed  entirely  satisfactory  in  regard  to  purity. 
They  were  all  examined  microscopically,  and  as  far  as  could  be 
judged  from  the  appearance  of  an  opaque  substance,  no  im- 
purities were  present.  The  samples  for  analysis  were  very 
carefully  pressed  upon  filter-paper  in  order  to  remove  the 
mother-liquor.  The  salt  is  practically  stable  in  the  air,  so  that 
decomposition  was  not  to  be  feared  during  the  drying  operation. 
Lead  and  potassium  were  determined  by  dissolving  the  sub- 
stance in  dilute  nitric  acid,  evaporating  with  sulphuric  acid, 
separating  the  lead  sulphate  by  filtration,  weighing  it,  and 
determining  potassium  in  the  filtrate  by  weighing  it  as  sul- 
phate. Iodine  was  determined  by  treating  the  substance  with 
a  solution  of  sodium  arsenite,  acidifying  with  nitric  acid, 
digesting  with  an  excess  of  silver  nitrate,  and  finally  weighing 
silver  iodide.  Carbon  and  hydrogen  were  determined  by 
combustion  with  lead  chromate,  where  the  front  part  of  the 
tube  contained  a  layer  of  metallic  silver  which  stopped  the 
passage  of  any  iodine. 


92  ON  SOME  COMPOUNDS   CONTAINING 

The  variations  in  the  results  of  the  analyses  are  consider- 
able, and  it  is  probable  that  the  salt,  being  always  deposited 
in  a  concentrated  mother-liquor,  was  never  quite  pure,  but 
there  is  no  evidence  that  the  variations  in  composition  have 
been  regularly  influenced  by  the  variations  in  the  conditions 
of  preparation.  The  analyses  are  given  in  the  order  in  which 
they  were  made.  The  last  three  probably  represent  better 
material  than  the  others. 


Lead. 

Potassium. 

Iodine. 

Carbon. 

Hydrogen. 

Oxygen 
(difference.) 

I 

35.51 

4.01 

37.50 

.   .    . 

... 

II 

36.24 

4.33 

36.16 

... 

.   •   . 

... 

III 

35.83 

4.32 

36.01 

.    .   . 

•   •    • 

•   •   • 

IV 

35.29 

4.07 

37.78 

•   .   . 

.    •    • 

•   • 

V 

36.21 

4.59 

.  .  . 

... 

... 

.    ,    . 

VI 

35.43 

4.20 

.  .  . 

.    .   • 

... 

.    •   • 

VII 

35.65 

4.40 

36.49 

... 

... 

... 

VIII 

35.35 

4.15 

.  .  . 

... 

... 

... 

IX 

34.80 

4.42 

.  .  . 

.   .    . 

... 

... 

X 

34.85 

3.93 

37.92 

9.14 

1.39 

12.77 

XI 

34.72 

3.97 

39.26 

9.17 

1.41 

11.47 

XII 

34.33 

3.94 

39.83 

8.77 

1.31 

11.82 

Calculated  for  5Pb(CH8CO2)2.3KI.6I, 

35.87        4.07        39.62         8.31         1.04        11.09 
Johnson  found, 

33.195      4.668      43.37         8.63         1.106        9.031 

It  must  be  admitted  that  the  results  do  not  agree  very  satis- 
factorily with  the  calculated  quantities,  and  that  the  formula 
is  somewhat  uncertain.  It  seems  probable,  however,  that  the 
compound  is  a  combination  of  lead  acetate  with  potassium 
triiodide  with  the  formula  5Pb(CH8CO2)2.3KI8.  It  is  not 
certain  that  the  extra  iodine  is  combined  with  the  potassium 
rather  than  with  the  lead,  but  since  KI8  is  a  well-known  com- 
pound, and  since  the  acetic  acid  radical  is  present  in  the 
proper  proportion  to  form  lead  acetate,  this  view  seems  to  be 
the  most  plausible  one. 


LEAD  AND  EXTRA   IODINE. 


93 


Johnson's  analysis  differs  chiefly  from  the  new  ones  in  its 
higher  iodine  and  consequently  lower  oxygen  as  determined 
by  difference.  His  oxygen  is  considerably  too  low  for  the 
amount  required  to  give  CH3CO2  with  the  carbon  and  hydro- 
gen, and  this  was  evidently  the  main  cause  of  his  inability  to 
arrive  at  a  rational  formula.  It  seems  probable  that  there  was 
an  error  in  his  determination  of  iodine. 

G-roger's  Salt  — A  compound  has  been  described  by  Max 
Groger  *  as  corresponding  to  the  remarkable  formula,  PbO. 
PbI2.I8.  As  he  prepared  it,  it  was  an  amorphous  precipitate 
which  had  been  washed  with  water,  and  exposed  to  the  air  for 
a  long  time  in  order  to  allow  iodine  with  which  it  was  mixed 
to  evaporate,  and,  consequently,  there  seemed  to  be  room  for 
doubt  as  to  its  freedom  from  decomposition  after  it  had  under- 
gone these  operations,  even  if  it  could  be  supposed  to  have 
been  a  pure  substance  when  it  was  precipitated. 

I  have  undertaken  a  reinvestigation  of  this  salt,  and  have 
succeeded  in  preparing  it  in  a  beautifully  crystalline  condition 
in  which  there  was  no  doubt  about  its  purity,  and  have  found 
that  Groger  really  analyzed  a  pure  compound,  but  that  he 
overlooked  some  water  that  it  contained.  With  the  addition 
of  one  molecule  of  water  his  formula  becomes  correct,  but  this 
formula,  Pb2I6O.H2O,  or,  as  it  may  be  written,  Pb2l5(OH)2,  is 
no  less  remarkable  than  the  one  which  Groger  advanced. 

This  substance,  in  a  crystallized  condition,  had  been  ob- 
served in  this  laboratory  a  short  time  before  Gro'ger's  work 
was  known  here.  At  my  suggestion,  Mr.  J.  H.  Pratt  had 
made  some  experiments  with  the  dark-colored  precipitate 
produced  by  mixing  strong  aqueous  solutions  of  lead  acetate 
and  potassium  triiodide.  Such  precipitates  were  collected 
upon  filters,  treated  while  still  moist  with  boiling  alcohol, 
and  the  resulting  liquid,  after  filtration,  was  evaporated  over 
sulphuric  acid,  with  the  result  that  small,  brilliant  black 
crystals  were  sometimes  obtained.  Several  partial  analyses  of 
this  substance  showed  that  it  contained  lead  and  iodine  in  the 
ratio  2  :  5,  and  were  as  follows  : 

*  Monatshefte  fur  Chemie,  xiii,  610, 1892. 


94  ON  SOME   COMPOUNDS   CONTAINING 


n.  in. 


Ratio  of         Calculated  for 


average.  Pb2I5O.H2O. 

Lead  .     .    .     37.84       .  .  .       37.32      2.00  38.23 

Iodine     .    .    57.66      58.71      58.62      5.07  58.63 

The  yield  of  this  product  was  very  small,  and  it  was  diffi- 
cult to  obtain  it  in  a  pure  condition,  since  it  was  often  mixed 
with  the  well-known  compound  PblOH,  and  with  other  sub- 
stances which  were  not  identified.  The  presence  of  water  in 
the  salt  was  established,  but  the  circumstances  were  such  that 
the  investigation  was  interrupted  at  a  point  where  the  pure 
material  at  hand  had  been  exhausted,  and  no  accurate  determi- 
nation of  water  had  been  made. 

My  thanks  are  due  to  Mr.  Pratt  for  his  valuable  assistance 
in  the  investigation  of  the  compound  up  to  this  point.  When 
I  subsequently  obtained  Groger's  salt  in  a  crystallized  condi- 
tion, it  proved  to  have  the  same  form  and  composition  as  the 
product  mentioned  above,  so  that  a  further  study  of  the  latter 
was  deemed  unnecessary. 

In  order  to  obtain  Groger's  compound  in  a  well-crystallized 
condition,  it  is  necessary  to  modify  his  method  of  preparation 
by  using  a  small  amount  of  acetic  acid.  It  is  also  advanta- 
geous to  use  boiling  water  instead  of  cold  water  for  the  pre- 
cipitation, and  to  use  a  somewhat  larger  volume  of  this  than 
is  recommended  by  him.  I  have  obtained  the  best  results  by 
the  following  method :  Dissolve  10  g.  iodine  in  100  c.  c. 
absolute  alcohol,  then  50  g.  crystallized  lead  acetate  in 
150  c.  c.  water,  3  c.  c.  glacial  acetic  acid,  and  300  c.  c.  absolute 
alcohol.  Mix  the  two  solutions,  let  stand  14  to  16  hours  at 
the  temperature  of  the  room,  filter  to  remove  the  small  pre- 
cipitate, then  dilute  with  1500  c.  c.  of  boiling  water.  Let  the 
whole  stand  until  cold,  when  the  compound  sought  will  have 
crystallized  out  mixed  with  iodine.  Pour  off  the  liquid  and 
wash  the  crystals  with  cold  alcohol  in  small  quantities  until 
the  iodine  is  removed.  Dry  the  product  upon  filter-paper,  and 
then  in  the  air  at  ordinary  temperature. 

The  product  consists  of  very  brilliant  black  crystals,  usually 
0.5  mm.  or  less  in  diameter.  They  form  octahedra,  appar- 


LEAD  AND  EXTRA   IODINE. 


95 


ently  of  the  tetragonal  system,  with  faces  that  are  much 
curved  and  otherwise  distorted.  The  powder  of  the  crystals 
is  similar  in  color  to  Groger's  precipitate,  and  it  agrees  with  it 
in  being  practically  stable  in  the  air  and  scarcely  acted  upon 
by  cold  water  or  alcohol. 

Two  separate  crops  of  apparently  perfect  purity  were 
analyzed.  Lead  and  iodine  were  determined  by  the  methods 
described  above  under  Johnson's  compound.  Water  was  col- 
lected and  weighed  in  a  calcium  chloride  tube,  the  substance 
being  ignited  in  a  tube  behind  a  layer  of  granulated  sodium 
carbonate  which  held  back  the  iodine  completely.  Free  iodine 
was  determined  volumetrically  by  the  use  of  sodium  thiosul- 
phate  solution.  The  results  were  as  follows : 


Lead  .  .  . 

Foi 
L 

.    3854 

ind. 

n. 
3822 

Calculated  for 
Pb2I6(OH),. 

Iodine  .  .  . 
Water  .  .  . 
Oxygen  (diff.)  . 

.    58.41 
.      1.83 
.       1.42 

58.62 
1.82 
1.34 

58.63 
1.66 
1.48 

100.00 

100.00 

100.00 

"  Free  "  iodine 
Loss  by  heating 


34.78 
36.43 


36.43    I8  +  H20 


35.18 
36.84 


I  have  also  prepared  the  compound,  exactly  according  to 
Groger's  directions,  as  a  reddish-brown  precipitate,  and  after 
the  product  was  apparently  free  from  intermixed  iodine  and 
air-dry,  it  was  dried  for  three  days,  spread  out  in  a  very  thin 
layer  under  a  bell-jar  well  charged  with  solid  potassium 
hydroxide.  This  product  gave  the  following  results  on 
analysis : 

Found. 

Water    ,  1.80 


Calculated  for 
Pb2I6(OH),. 

1.66 


This  result  indicates  that  Grb'ger  overlooked  water  in  his 
compound,  and  that  his  precipitate  is  identical  with  the  crys- 
tallized product. 

I  have  observed  the  formation  of  this  salt,  under  various  con- 
ditions, when  alcoholic  solutions  containing  lead  acetate  and 


96      COMPOUNDS   CONTAINING  LEAD  AND  IODINE. 

iodine,  and  in  some  cases  potassium  iodide  also,  were  diluted, 
but  the  purest  crops  have  been  obtained  only  when  the  ingre- 
dients were  used  nearly  in  the  proportion  which  Grb'ger  recom- 
mends, and  also  when  the  alcoholic  mixture  has  been  allowed 
to  stand  for  the  proper  period.  The  compound  cannot  be 
recrystallized  from  water,  alcohol,  or  mixtures  of  the  two 
liquids,  and  it  seems  probable,  as  Groger  suggests,  that  it  is 
formed  by  the  decomposition  of  some  other  compound  by 
water.  This  view  does  not  conflict  with  the  fact  that  it  was 
prepared,  as  described  above,  by  the  evaporation  of  certain 
alcoholic  solutions,  because  these  always  contained  water  which 
increased  in  proportion  to  the  alcohol  as  the  evaporation  went 
on.  The  presence  of  an  acetate  seems  to  be  indispensable  to 
its  production,  for  I  have  made  a  number  of  experiments  using 
lead  nitrate  instead  of  the  acetate  with  no  indication  of  its 
formation.  It  seems  probable  that  a  soluble  compound  closely 
related  to  Johnson's  salt  is  formed  at  first,  and  that  this  yields 
Groger's  compound  by  the  action  of  water. 

I  have  made  unsuccessful  attempts  to  prepare  a  bromide 
corresponding  to  Groger's  salt,  and  my  attempts  to  replace  a 
part  of  the  iodine  in  it  by  bromine  have  also  failed. 

Conclusion. —  The  two  compounds  which  have  been  re-inves- 
tigated, 5Pb(CH3CO2)2.3KI.6I  and  PbI2.PbO.3I.H2O,  show 
no  evident  relation  to  each  other  nor  to  the  compound  2PbI2. 
8KI.L4HiO,  which  I  have  previously  described,  except  that 
all  of  them  are  of  complicated  composition  and  they  all  con- 
tain extra  iodine  without  showing  evidence  of  the  existence  of 
lead  tetraiodide.  Classen  and  Zahorski's  quinoline  salt,  pre- 
viously referred  to,  seems  to  furnish  the  only  evidence  of  the 
existence  of  this  higher  iodide  in  combination. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
March,  1895. 


ON  THE  VOLUMETRIC  DETERMINATION  OF 
TITANIC  ACID  AND  IRON  IN  ORES.* 

BY  H.  L.  WELLS  AND  W.  L.  MITCHELL. 

THE  difficulties  connected  with  the  gravimetric  determination 
of  titanic  acid  make  a  reliable  volumetric  method  very  desir- 
able, especially  for  the  analysis  of  titanic  iron  ores.  We  have 
therefore  turned  our  attention  to  this  subject,  and  have  found 
that  satisfactory  results  can  be  obtained  by  a  slight  modification 
of  a  process  which  has  long  been  known. 

About  thirty  years  ago  F.  Pisanif  stated  that  the  acid  under 
consideration  could  be  determined  by  reduction  with  zinc  in 
hydrochloric  acid  solution,  using  a  gentle  heat,  and  when  the 
violet  color  no  longer  deepened,  pouring  off  the  liquid  from  the 
remaining  zinc  and  titrating  with  potassium  permanganate. 
Pisani  gave  no  test  analyses,  and,  since  his  process  has  not 
been  generally  adopted,  it  is  evident  that  it  has  not  proved 
satisfactory  in  the  hands  of  others. 

A  number  of  years  ago  one  of  us  (Wells)  had  occasion  to 
analyze  a  large  number  of  titanic  iron  ores,  and  attempted  to 
use  Pisani's  method  with  the  use  of  sulphuric  acid  instead  of 
hydrochloric  acid,  as  recommended  by  the  originator  of  the 
process.  This  modification  was  made  on  account  of  the  well- 
known  interference  of  chlorides  with  the  permanganate  method, 
and  it  was  found  that  the  difficulty  mentioned  by  Pisani,  that 
titanic  acid  was  liable  to  be  precipitated  by  heating  sulphate 
solutions,  could  be  readily  overcome  by  using  a  sufficiently 
large  quantity  of  sulphuric  acid.  The  results  of  a  great  many 
trials  at  that  time,  however,  showed  that  the  method  gave  very 
low  results,  and  the  process  was  then  abandoned.  The  process 
used  in  the  experiments  just  referred  to  was  precisely  the  same 

*  Jour.  Amer.  Chem.  Soc.,  xvii,  November,  1895. 
t  Compt.  rend.,  lix,  289. 
7 


98  DETERMINATION  OF  TITANIC  ACID 

as  that  which  we  now  recommend  and  which  will  be  described 
in  detail  below,  except  that,  after  reduction  with  zinc,  the  solu- 
tion was  poured  off  from  the  excess  of  that  metal  into  a  beaker 
for  titration,  an  operation  which  Pisani  recommended,  and 
which  is  customary  in  the  determination  of  iron  by  this 
method.  It  is  now  evident  that  the  failure  of  the  method  was 
due  to  the  contact  of  the  solutions  with  atmospheric  air,  for, 
while  ferrous  sulphate  is  acted  upon  very  slowly,  the  sulphate 
corresponding  to  the  lower  oxide  of  titanium  is  very  rapidly 
oxidized  under  such  circumstances. 

Marignac,*  with  his  accustomed  skill,  applied  Pisani's 
method,  soon  after  its  publication,  to  the  determination  of 
titanic  acid  in  the  presence  of  niobic  acid.  He  was  obliged  to 
use  special  conditions  in  order  to  avoid  the  reduction  of  the 
other  acid  at  the  same  time,  but  the  feature  of  his  process  which 
is  interesting  in  the  present  connection  is,  that  he  reduced  the 
titanic  acid  by  means  of  a  long  rod  of  pure  zinc  extending  up 
into  the  neck  of  the  flask  which  held  the  solution,  and,  after 
allowing  the  reduction  to  take  place  out  of  contact  with  air, 
he  finally  took  out  the  zinc  and  titrated  directly  in  the  flask 
without  transferring.  Marignac  gave  a  number  of  test  analy- 
ses which  showed  that  the  method  gave  very  good  results, 
although  they  were  a  little  too  low  with  the  larger  quantities 
of  titanic  acid  used. 

We  have  modified  the  method  of  Pisani,  as  improved  by 
Marignac,  by  using  sulphuric  acid  solutions  and  by  protecting 
the  liquid  during  cooling  and  titration  by  means  of  carbon 
dioxide,  and  we  have  also  arranged  the  process  for  the  deter- 
mination of  iron  along  with  the  titanic  acid.  The  details  of 
the  operation  are  as  follows : 

Five  grams  of  very  finely  pulverized  ore  are  placed  in  a  rather 
large  beaker,  covered  with  a  watch-glass,  and  treated  with  about 
100  c.  c.  of  concentrated  hydrochloric  acid.  A  very  gentle, 
gradually  increasing  heat  is  applied  for  several  hours,  more 
hydrochloric  acid  is  added  if  necessary,  and,  when  no  further 
action  is  apparent,  about  50  c.  c.  of  a  mixture  of  equal  volumes 

*  Zeitschr.  anal.  Chem.,  vii,  112. 


AND  IRON  IN  ORES.  99 

of  concentrated  sulphuric  acid  and  water  are  added,  and  the 
whole  is  evaporated  until  the  sulphuric  acid  fumes  strongly. 
After  cooling,  about  200  c.  c.  of  water  are  added,  the  whole  is 
heated  until  the  sulphates  are  dissolved,  and  the  liquid  is  filtered 
into  a  liter  flask.  With  many  titanic  ores  this  operation  will 
have  dissolved  everything  except  siliceous  matter.  If,  however, 
some  undissolved  ore  remains,  it  is  ignited,  to  burn  the  filter- 
paper,  in  a  platinum  crucible,  and  the  residue  is  fused  with 
potassium  disulphate,  at  a  gradually  increasing  heat,  up  to  low 
redness,  until  the  black  particles  have  disappeared.  To  the 
cake  in  the  crucible  several  volumes  of  concentrated  sulphuric 
acid  are  added,  heat  is  gradually  applied  until  the  whole 
becomes  liquid,  then  this  is  heated  with  a  moderate  volume  of 
water  to  dissolve  the  sulphates,  and  the  liquid  is  added  to  the 
main  solution  in  the  liter  flask.  Filtration  may  be  omitted 
here,  or  in  the  case  of  the  original  solution,  provided  that  the 
siliceous  matter  is  not  to  be  weighed. 

The  liquid  in  the  liter  flask  is  diluted  to  the  mark  and  mixed, 
and  four  portions  of  200  c.  c.  each,  representing  1  g.  of  ore, 
are  taken,  two  of  them  into  Erlenmeyer  (conical)  flasks  of 
500  c.  c.  capacity,  and  the  other  two  into  ordinary  flasks  of 
350  c.  c.  capacity. 

To  determine  iron,  hydrogen  sulphide  is  passed  into  the  solu- 
tions in  the  ordinary  flasks  until  they  are  saturated  with  the 
gas,  then  inverted  porcelain  crucible  covers  are  placed  upon 
the  mouths  of  the  flasks,  and  the  solutions  are  heated  and 
boiled  continuously,  so  that  air  cannot  enter,  until  the  hydro- 
gen sulphide  has  been  completely  removed.  This  point  can 
be  determined  by  testing  the  escaping  steam  with  paper  which 
has  been  dipped  in  a  solution  of  lead  acetate  made  strongly 
alkaline  with  potassium  hydroxide.  The  flasks  are  then 
quickly  filled  to  the  neck  with  cold  distilled  water  (which  has 
been  recently  boiled),  best  by  means  of  an  inverted  wash-bottle, 
directing  the  stream  against  the  neck  of  the  flask  in  such  a 
way  that  the  water  does  not  mix  to  a  great  extent  with  the 
heavier  sulphuric  acid  solution.  If  the  stream  of  cold  water 
does  not  strike  the  top  of  the  neck,  there  is  little  danger  of 


100  DETERMINATION  OF  TITANIC  ACID 

breaking  the  hot  glass.  The  contents  of  the  flasks  are  now 
rapidly  cooled  by  means  of  a  stream  of  water,  transferred  to 
large  beakers,  and  titrated  with  potassium  permanganate 
solution. 

To  the  solutions  in  the  Erlenmeyer  flasks,  about  25  c.  c. 
of  concentrated  sulphuric  acid  are  added,  then,  in  each  case, 
three  or  four  rods  of  chemically  pure  zinc,  about  50  mm.  long 
and  6  or  7  mm.  in  diameter,  are  attached  to  the  loop  of  a 
porcelain  crucible  cover,  which  is  larger  than  the  mouth  of  the 
flask,  by  means  of  platinum  wire  wound  securely  around  them 
near  the  middle.  The  length  of  the  wire  is  so  arranged  that 
the  pieces  of  zinc  will  be  suspended  in  the  liquid  when  the 
cover  is  placed  on  the  flask.  When  this  has  been  accom- 
plished, the  liquid  is  boiled  gently,  so  as  to  keep  out  air,  for 
thirty  or  forty  minutes,  then,  without  interrupting  the  boiling, 
a  glass  tube,  so  bent  that  it  extends  50  mm.  or  more  into  the 
flask,  and  which  is  deli vering  a  rather  rapid  stream  of  carbon 
dioxide,  is  introduced  under  the  cover.  Care  should  be  taken 
to  have  the  carbon  dioxide  free  from  air,  and  that  hydrochloric 
acid  which  contains  sulphur  dioxide  is  not  used  for  its  gener- 
ation. The  flask  is  now  rapidly  cooled,  and  then  the  zinc  is 
washed  with  a  jet  of  water  and  removed,  and  the  solution  is 
titrated  with  permanganate  in  the  flask  while  the  carbon  di- 
oxide is  still  being  passed  in.  The  difference  between  the 
permanganate  used  in  this  case  and  that  used  for  the  iron 
alone,  represents  the  amount  corresponding  to  the  titanic  acid. 
The  factor  for  metallic  iron  divided  by  0.7  gives  the  factor  for 
titanic  acid  (TiO2). 

When  a  50  c.  c.  burette  is  used,  the  most  convenient 
strength  for  the  permanganate  solution  is  when  1  c.  c.  is  equal 
to  about  0.014  g.  of  metallic  iron,  corresponding  to  7.9  g. 
of  potassium  permanganate  per  liter. 

It  is  customary  in  this  laboratory  to  standardize  permanga- 
nate solutions  by  a  method  which  very  closely  approaches  the 
one  described  above  for  the  actual  determination  of  iron,  so 
that,  if  any  slight  errors  are  inherent  in  the  process,  they  are 
likely  to  be  eliminated  because  they  have  an  equal  effect  upon 


AND  IRON  IN  ORES.  101 

the  standardization  and  the  determination.  The  method  is 
simple  and  convenient,  and  a  large  amount  of  experience  has 
shown  it  to  be  very  accurate.  To  carry  out  this  operation,  a 
350  c.  c.  flask  is  half  filled  with  sulphuric  acid  (the  strong  acid 
diluted  with  about  eight  volumes  of  water).  This  is  heated  to 
boiling  with  an  inverted  crucible  cover  upon  the  mouth  of  the 
flask,  and,  after  the  air  had  been  expelled,  about  0.6  g.  of 
the  purest  iron  wire,  representing  nearly  the  average  amount 
of  iron  in  1  g.  of  an  ore,  is  dropped  in,  and  gentle  boiling 
is  continued  until  it  has  dissolved.  The  flask  is  filled  to  the 
neck  with  water,  cooled,  and  finally  the  liquid  is  transferred 
to  a  beaker  and  titrated. 

The  method  of  determining  iron  by  reduction  with  hydrogen 
sulphide,  although  well  known,  does  not  appear  to  be  as  gener- 
ally used  as  it  deserves  to  be.  The  precipitated  sulphur  present 
in  the  liquid  has  absolutely  no  effect  upon  cold  permanganate 
solution,  but  precipitated  sulphides,  such  as  copper  sulphide, 
should  be  filtered  off  before  boiling.  Since  concentrated  sul- 
phuric acid  is  an  oxidizing  agent,  care  must  be  taken  to  use 
sufficiently  dilute  solutions,  and  not  boil  them  down  until  the 
acid  becomes  strong. 

Potassium  titanofluoride  Titanium  Titanium  TJWm. 

taken.  found.  calculated. 

0.7638  0.1437  0.1527  -0.0090 

0.6425  0.1225  0.1285  -0.0060 

0.7778  0.1524  0.1555  —0.0031 

0.6793  0.1308  0.1358  -0.0050 

0.8226  0.1607  0.1645  -0.0038 

1.0956  0.2107  0.2191  -0.0084 

0.4451  0.0848  0.0890  -0.0042 

0.6359  0.1215  0.1271  -0.0056 

0.9004  0.1715  0.1800  -0.0085 

0.4634  0.0882  0.0926  -0.0044 

We  have  made  some  test  analyses  upon  the  method  of  de- 
termining titanic  acid  volumetrically.  Crude  potassium  titano- 
fluoride, K2TiF«,  was  recrystallized  twice  from  water  and  used 
as  the  source  of  titanium.  Weighed  quantities  of  the  care- 


102  TITANIC  ACID  AND  IRON  IN  ORES. 

fully  dried  salt  were  evaporated  with  sulphuric  acid,  and  the 
resulting  substance  was  treated  essentially  as  has  been  de- 
scribed above,  but  with  some  variations  in  the  time  of  boiling, 
the  strength  of  the  acid,  and  the  amount  of  zinc  used.  The 
table  on  page  101  gives  the  results  obtained  in  grams. 

The  results  show  a  fair  degree  of  uniformity,  but  they  are 
invariably  too  low.  A  part  of  the  deficiency  was  probably 
due  to  the  impurities  in  the  potassium  titanofluoride  used,  for 
it  is  quite  possible  that  certain  impurities  may  have  been  in- 
creased rather  than  diminished  by  recrystallizing  it,  and  it  is 
exceedingly  difficult  to  obtain  any  titanium  compound  that 
is  certainly  free  from  all  other  acid-forming  elements.  The 
greater  portion  of  the  error  was  doubtless  due  to  the  action  of 
air  which  gained  access  to  the  liquid  in  spite  of  the  precautions 
used,  and  it  is  evident  that  the  accuracy  of  determinations 
made  by  this  method  would  be  increased  by  adding  one- 
twentieth  or  one-thirtieth  to  the  amount  of  titanic  acid 
found  under  the  conditions  that  we  have  used. 

The  great  influence  of  the  action  of  air  is  shown  by  two 
determinations  which  were  made  exactly  like  those  given  in 
the  preceding  table,  except  that,  after  cooling  in  carbon 
dioxide,  the  solutions  were  transferred  to  beakers  and  titrated 
as  quickly  as  possible. 

Potassium  titanofluoride         Titanium  Titanium  ,, 

taken.  found.  calculated. 

0.6831  0.1078  0.1366  0.0288 

0.9545  0.1535  0.1909  0.0374 

The  volumetric  method,  even  without  correction,  will  be 
likely  to  give  more  reliable  results  than  those  obtained  by 
gravimetric  determination,  unless  great  care  and  skill  are 
displayed  in  carrying  out  the  latter. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
October,  1895. 


ON  SOME  COMPOUNDS  OF  TRIVALENT 
VANADIUM.* 

BY  JAMES  LOCKE  AND  GASTON  H.  EDWARDS. 

THE  green  solution  obtained  when  vanadic  acid  is  reduced  by 
nascent  hydrogen  has  been  but  very  slightly  studied.  That 
it  contains  salts  of  vanadium  in  the  trivalent  state  was  recog- 
nized by  Roscoef  in  the  course  of  his  elaborate  investigation 
on  the  chemical  nature  of  this  element.  Roscoe,  however, 
made  no  attempt  to  study  the  products  which  could  be  obtained 
from  the  solution  which  he  prepared  by  dissolving  the  anhy- 
drous chloride,  VC13,  in  water,  and  failed  to  make  any  compari- 
son between  that  body  and  the  chlorides  of  other  trivalent 
elements. 

The  first  compounds  to  be  isolated  from  a  vanadic  solution 
were  prepared  by  Petersen,J  who  examined  in  a  very  thorough 
manner  the  fluoride  and  its  double  salts  with  the  fluorides  of 
other  metals.  His  results  pointed  to  a  close  resemblance 
between  vanadium  sesquioxide  and  its  derivatives  and  the 
compounds  of  the  groups  formed  by  aluminium,  chromium 
manganese,  and  iron.  Thus,  the  compound  K2VF5.H2O 
exhibits  in  its  general  properties,  solubility,  etc.,  close  simi- 
larity to  the  analogously  constituted  salts  of  aluminium,  iron, 
chromium,  and  manganese.  Ammonium  vanadifluoride, 
(NH4)8VF6,  is  isomorphous  with  the  ferric  salt,  (NH4)8FeF6, 
described  by  Marignac,§  and  Petersen  prepared  other  members 
of  the  series  in  (NH4)8CrF6  and  (NH4)8A1F6.  A  similar 
relation  was  observed  between  double  salts  with  the  fluorides 
of  divalent  metals,  such  as  CoVF5.7H2O,  CoCrF6.7H2O,  etc. 

*  Amer.  Chem.  Jour.,  xx,  July,  1898. 

t  Ann.  Chem.  (Liebig),  Suppl.,  vii,  78. 

t  J.  prakt.  Chem.  (2),  xl,  44  (1889).  §  Ann.  china,  phys.,  (3)  Ix,  306. 


104  ON  SOME   COMPOUNDS   OF 

Petersen's  work  and  the  conclusions  drawn  from  his  results 
were  further  substantiated  by  the  recent  investigations  of 
Piccini*  on  the  alums  of  vanadium.  He  succeeded  in  isolating 
the  salts  NaV(SO4)2.12H2O,  KV(SO4)2.12H2O,  NH4V(SO4)2. 
12H20,  RbV(S04)2.12H20,  CsV(SO4)2.12H2O,  and  T1VSO42. 
12H2O.  With  the  exception  of  a  short  article  by  Brieiiy,f 
who  prepared  a  vanadium  sulphuric  acid,  or  '  alum  acid,'  J 
V(SO4)SO4H.4H2O,  the  above  investigations  embrace  practi- 
cally all  that  has  been  published  on  vanadic  salts. 

We  have  recently  undertaken  the  preparation  of  a  number 
of  other  compounds,  the  analogues  of  which  are  of  character- 
istic nature  in  the  case  of  chromium,  in  the  hope  of  ascertain- 
ing more  definitely  the  influence  which  the  atomic  weight  of 
vanadium  exerts  upon  the  development  of  the  properties  com- 
mon to  the  compounds  of  the  group :  aluminium,  vanadium, 
chromium,  manganese,  iron,  and  cobalt. 

The  chief  difficulty  which  an  investigation  of  this  kind  pre- 
sents lies  in  the  extreme  readiness  with  which  vanadic 
solutions  absorb  oxygen,  with  formation  of  vanadyl  salts. 
Petersen  was  able  to  start  directly  from  the  anhydrous  sesqui- 
oxide,  which  is  soluble  in  hydrofluoric  acid.  The  solutions  of 
vanadic  sulphate  used  by  Piccini  in  the  preparation  of  the 
alums  were  obtained  simply  by  the  electrolysis  of  vanadic  acid 
in  a  solution  of  sulphuric  acid.  These  methods,  while  sat- 
isfactory in  individual  cases,  are  of  course  limited  in  their 
applicability,  and  they  could  not  be  used  in  the  preparation 
of  such  compounds  as  a  vanadicyanide,  sulphocyanate,  or  the 
like.  We  were  therefore  compelled  to  start  out  from  the 
readily  oxidizable  vanadic  hydroxide,  precipitated  by  an  alkali 
after  the  reduction  of  the  pentoxide  with  sodium  amalgam. 

In  order  to  protect  the  hydroxide  and  solutions  from  oxi- 
dation, all  operations  were  carried  out  in  an  atmosphere 
of  hydrogen.  For  this  purpose  the  apparatus  shown  in  the 

*  Zeitschr,  anorg.  Chem.,  xi,  106  ;  xiii,  441. 
t  J.  Chem.  Soc.  (London),  xlix,  822. 

t  Chromium  is  the  only  other  alum-forming  metal  which  yields  such  an 
acid,  Cr(S04)S04H. 


TRIVALENT   VANADIUM. 


105 


accompanying   figure  was  employed.     The   pear-shaped   bulb 
a,  of  which  we  had  several  pieces,  holds  about  500  c.  c.     Over 


its  drawn-out  end,  which  is  two-thirds  of  an  inch  in  diameter, 
passes  a  piece  of  thick-walled,  soft-rubber  tubing,  which  can 
be  closed  by  a  stop-cock  e.  The  tube  b  is  of  capillary  diameter, 
fitted  with  a  glass  cock,  and  bent  over  on  itself,  to  more 
securely  prevent  the  entrance  of  air  when  this  cock  is  open, 
c  is  a  somewhat  wider  tube,  which  serves  for  the  introduction 
of  reagents,  and  is  closed  by  a  stop-cock  when  necessary. 

For  heating  on  the  water-bath,  the  bulb  is  placed  on  the 
latter,  mouth  downward,  while  a  rapid  current  of  hydrogen  is 
passed  in  at  <?,  a  being  open.  The  contents  of  the  bulb  may 
be  boiled  in  a  similar  manner,  the  bulb  then  resting  on  its 


106  ON  SOME   COMPOUNDS  OF 

side.  Reagents  are  added  by  means  of  a  small  flask  m,  fitted 
with  a  cork  holding  two  short  tubes,  one  of  which  is  connected 
with  the  hydrogen  generator.  The  reagent  having  been  intro- 
duced into  the  flask  (a  test-tube  is  also  convenient)  the  air  in 
the  latter  is  displaced  by  hydrogen,  and  the  second  tube  then 
connected  with  <?.  The  flask  is  then  simply  inverted,  where- 
upon the  reagent  runs  into  the  bulb. 

The  most  important  and  difficult  operation  involved  in  the 
work  was  of  course  the  filtration  and  washing  of  the  vanadic 
hydroxide.  To  perform  this  without  exposing  the  substance 
to  the  air,  a  Buchner's  funnel  was  used,  to  which  was  joined  by 
a  wide  rubber  band  a  well-fitting  piece  of  apparatus,  d,  like  an 
inverted  funnel.  The  stem  of  the  latter  was  of  the  same 
diameter  as  the  mouth  of  the  bulb.  Before  attaching  this 
filtering-apparatus  to  the  bulb,  it  was  entirely  filled,  together 
with  the  suction-flask,  with  water,  and  the  latter  then  dis- 
placed by  hydrogen.  Connection  was  then  made,  slight 
suction  applied,  and  the  stop-cock  at  the  mouth  of  the  bulb 
opened.  The  precipitate  was  washed  with  water  from  which 
the  air  had  been  expelled  by  boiling,  from  a  flask  connected  as 
for  the  introduction  of  reagents. 

When  the  next  operation  involved  the  solution  of  the  pre- 
cipitate in  an  acid,  the  filtrate  was  drawn  off  by  suction 
through  the  pump,  the  suction-flask  rinsed  with  the  water  from 
one  or  two  additional  washings,  and  the  acid  then  introduced 
as  above.  The  solution  was  then  transferred,  either  to  another 
bulb,  or,  if  it  was  to  be  evaporated  to  crystallization,  to  a 
crystallizing-dish,  the  side  tube  of  the  suction-flask  being  in 
that  case  held  below  the  surface  of  some  benzine  placed  in 
the  dish. 

By  taking  proper  care  in  the  observance  of  minor  details, 
such  as  the  filling  of  the  tubes  with  water  before  making  connec- 
tions, etc.,  we  were  able  almost  entirely  to  obviate  the  danger 
of  oxidation ;  and  after  a  little  practice  we  could  carry  out  the 
operations  of  filtration  and  the  like  almost  as  rapidly  as  in 
the  open  air.  In  one  afternoon,  starting  out  with  vanadium 
pentoxide,  we  have  prepared  vanadium  dihydroxide,  V(OH)2, 


TRIVALENT   VANADIUM. 


107 


washed  it,  redissolved  in  hydrochloric  acid,  and  brought  the 
solution  into  a  desiccator.  In  spite  of  all  the  operations  sub- 
sequent to  the  reduction  of  the  vanadic  acid,  the  final  solution 
possessed  the  true  lavender  color  of  vanadious  salts,  without 
a  trace  of  green  or  brown.  Roscoe  describes  such  a  solution 
as  being  a  more  sensitive  reagent  towards  oxygen  than  is 
pyrogallol  itself. 

The  vanadium  preparations  which  we  used  in  this  work 
were  placed  at  our  disposal  through  the  kindness  of  Prof. 
Paul  Jannasch,  of  Heidelberg,  Germany.  They  consisted 
chiefly  of  thoroughly  purified  vanadates  of  sodium  and  am- 
monium. These  compounds  were  worked  up  as  follows : 
Enough  of  the  substance  to  yield  about  5  g.  of  vanadium 
hydroxide  was  dissolved  in  a  small  quantity  of  water,  10  c.  c. 
of  concentrated  hydrochloric  acid  were  added,  and  the  solu- 
tion boiled  with  alcohol  to  reduce  the  vanadic  acid  to  vanadyl 
dichloride,  VOC12.  After  the  alcohol  had  been  driven  off, 
the  solution  was  transferred  to  a  bulb,  and  while  a  rapid  cur- 
rent of  hydrogen  was  led  through  the  latter,  5  per  cent 
sodium  amalgam  was  gradually  introduced  hi  small  lumps, 
the  solution  being  in  the  meantime  kept  acid  by  the  occa- 
sional addition  of  hydrochloric  acid.  The  reduction  was  con- 
tinued until  the  solution  just  began  to  lose  the  pure  green 
color  of  the  vanadic  salts  and  assume  a  bluish-green  tint,  due 
to  compounds  of  the  next  lower  degree  of  oxidation.  The 
operation  required  the  addition  of  about  700  g.  of  amalgam. 

The  mercury  was  next  drawn  off,  the  solution  filtered, 
transferred  to  another  bulb,  and  treated  in  the  cold  with  just 
enough  ammonium  hydroxide  to  precipitate  the  vanadic  hy- 
droxide *  completely.  The  latter  comes  down  as  a  dirty  green 
flocculent  precipitate,  which  absorbs  oxygen  with  the  greatest 
avidity.  It  was  allowed  to  stand  for  some  tune,  and  then  fil- 
tered and  washed  thoroughly  with  warm  water  from  which 
the  air  had  been  expelled.  From  this  precipitate  the  follow- 
ing salts  were  obtained  by  solution  and  crystallization. 

*  Potassium  hydroxide  does  not  work  as  well  for  this  purpose,  as  it  dis- 
solves more  or  less  of  the  vanadic  hydroxide. 


108  ON  SOME   COMPOUNDS  OF 

Vanadium  Trichloride,  VCl^GH^.  0.  —  Halberstadt  *  men- 
tions the  fact  that  when  the  anhydrous  chloride,  VC13,  is  dis- 
solved in  water  and  the  solution  evaporated  over  sulphuric 
acid,  a  very  unstable  crystalline  compound  is  obtained.  Pic- 
cini  mentions  in  a  foot-note  to  his  first  article  on  the  vana- 
dium alums  f  that  he  had  obtained  this  substance  in  distinct 
crystals,  and  found  it  to  have  the  above  composition.  This 
foot-note  escaped  our  notice  when  first  reading  his  article,  and 
at  the  time  of  preparing  the  compound  we  supposed  we  were 
the  first  to  have  isolated  it.  As,  however,  nearly  three  years 
have  elapsed  since  his  article  was  sent  in  for  publication,  we 
may  be  allowed  to  describe  the  compound,  yielding  to  him  the 
priority  of  its  discovery. 

It  is  obtained  by  dissolving  vanadic  hydroxide  in  concen- 
trated hydrochloric  acid  and  evaporating  the  green  solution 
to  dryness  in  a  vacuum-desiccator.  The  salt  separates  out 
from  the  syrupy  liquid  in  large  green  prisms,  some  of  which 
attained  with  us  the  length  of  nearly  half  a  centimeter.  It 
dissolves  in  water  with  extreme  readiness,  yielding,  like  the 
other  neutral  vanadic  salts,  a  brown  solution  which  becomes 
green  on  acidification.  The  salt  is  very  deliquescent,  and  on 
exposure  to  the  air  for  any  length  of  time,  dissolves  in  the 
water  absorbed  and  is  oxidized  to  vanadyl  dichloride.  It  is 
readily  soluble  in  both  alcohol  and  ether,  but  no  distinct  crys- 
tals could  be  obtained  from  its  solution  in  these  liquids. 

In  the  analysis  of  the  substance  the  solution  was  acidified 
with  nitric  acid  and  the  chlorine  precipitated  with  silver  nitrate. 
The  vanadium  was  determined  in  another  portion  by  titra- 
tion  from  the  tetravalent  to  the  pentavalent  state  with  iodine, 
according  to  Browning's  J  method.  The  water  was  estimated 
by  difference :  - 

Calculated  for  •.,        , 

VC13.6H20.  Found. 

V 19.24  18.96 

Cl      ....    40.10  39.95 

H20  ....     40.66  41.09 

100.00  100.00 

*  Ber.  d.  chem.  Ges.,  xv,  1619  (1882). 

t  Zeitschr.  anorg.  Chem.,  xi,  107  (1896).  |  Ibid.,  i,  158. 


TRIVALENT  VANADIUM. 


109 


An  attempt  was  made  to  measure  the  crystals,  but  they 
proved  too  hygroscopic.  Their  optical  properties,  however, 
were  found  to  conform  to  the  rhombic  system.  Salts  of  com- 
position similar  to  that  of  this  compound  are  seen  in  A1C13. 
6H2O,  CrCl3.6H2O,  and  FeCl3.6H2O. 

Potassium  Vanadichloride.  —  An  attempt  was  made  to  pre- 
pare from  the  chloride  a  double  salt  analogous  to  those  of  the 
series  R2FeCl5.H2O,  in  which  R  is  K,  Rb,  NH4,  etc.  A  few 
grams  of  the  trichloride  were  dissolved  in  concentrated  hydro- 
chloric acid,  the  calculated  quantity  of  potassium  chloride  added, 
and  the  mixture  left  to  crystallize  in  a  vacuum.  The  product 
consisted  chiefly  of  green  crystals  of  a  somewhat  lighter  shade 
than  that  of  the  pure  vanadium  chloride,  but  it  was  impos- 
sible to  isolate  these  completely.  A  vanadium  determination, 
made  in  as  pure  a  product  as  we  could  obtain,  showed  that  it 
contained  22.41  per  cent  V.  The  quantity  calculated  for  the 
anhydrous  compound  KVC14  is  22.03  per  cent  V. 

Vanadium  Bromide,  VBr3.6H2  0.  —  This  compound  was 
prepared  in  a  manner  strictly  analogous  to  that  by  which  the 
chloride  was  obtained,  pure  concentrated  hydrobromic  acid 
being  used.  It  crystallizes  with  less  readiness  than  the 
chloride,  and  decomposes  more  easily.  In  other  respects  the 
two  compounds  were  closely  similar.  The  bromide  decom- 
poses more  or  less  on  solution  in  water,  leaving  as  a  residue 
a  small  quantity  of  a  brown  substance,  probably  a  basic  bro- 
mide. Like  the  chloride,  it  is  soluble  in  both  alcohol  and 
ether,  to  a  green  solution.  The  analysis  was  carried  out  as 
in  the  case  of  the  chloride. 


V  . 
Br 

H20 


Calculated  for 
VBr8  -f-  6H2O. 

,  12.83 
60.10 
27.07 


100.00 


The  iodide  could  not  be  obtained.  Vanadium  hydroxide 
dissolves  in  hydriodic  acid  as  readily  as  in  hydrochloric  or 
hydrobromic,  but  the  solution  turns  brown  on  evaporation 


110  ON  SOME   COMPOUNDS   OF 

and  eventually  leaves  only  an  amorphous,  brownish-black 
residue,  only  partially  soluble  in  water. 

Potassium  Vanadicyanide,  Kz  V(  CN^)6. —  For  the  preparation 
of  this  compound,  it  was  found  more  convenient  to  start  out 
from  the  anhydrous  vanadium  trichloride,  which  we  prepared 
according  to  the  method  of  Halberstadt.*  About  5  g.  of 
this  substance  were  dissolved  in  as  little  water  as  possible  f 
and  slightly  acidified  with  hydrochloric  acid.  A  concentrated 
solution  of  potassium  cyanide  containing  about  one  and  a  half 
times  the  calculated  quantity  of  the  salt  was  placed  hi  a  bulb, 
and  the  vanadium  chloride  solution  then  added.  The  mixture 
at  once  assumed  the  form  of  a  thick,  deep-purple  paste  which 
gradually  became  thin  again,  though  without  at  first  losing  its 
color,  and  remaining  almost  opaque.  This  part  of  the  reaction 
was  observed  by  Petersen,J  who  states  that  he  thus  obtained 
a  dark  blue  solution.  The  blue  color,  however,  is  in  fact  due 
only  to  very  finely  divided  particles  of  the  original  precipitate 
suspended  in  the  solution,  which  is  itself  of  a  deep  wine  color. 
After  shaking  for  some  time,  the  liquid  cleared,  and  only  a 
few  flakes  of  a  brown  residue,  presumably  the  hydroxide, 
remained  undissolved.  It  is  absolutely  necessary  to  have  a 
considerable  excess  of  potassium  cyanide  present,  as  the  pre- 
cipitate dissolves  with  great  difficulty,  and  a  clear  solution 
cannot  otherwise  be  obtained. 

The  wine-colored  solution,  after  being  filtered,  was  treated 
with  just  enough  alcohol  to  bring  about  incipient  precipitation, 
and  then  allowed  to  stand  for  some  hours  surrounded  by  ice- 
water.  A  fine  precipitate  separated  out,  which  consisted  of  a 
mixture  of  potassium  cyanide  and  vanadicyanide,  and  in  addi- 
tion to  this,  comparatively  large  crystals  of  the  latter  collected 
on  the  sides  and  bottom  of  the  vessel.  These  alone  were 

*  Ber.  d.  chem.  Ges.,  xv,  1619  (1882). 

t  The  formation  of  the  hydrated  chloride  is  readily  seen  when  a  quantity 
of  the  anhydrous  chloride  is  added  to  about  its  own  volume  of  water.  It  dis- 
solves with  a  hissing  sound,  and,  on  cooling,  the  liquid  solidifies  to  a  green 
crystalline  mass.  On  addition  of  more  water,  this  dissolves  to  a  brown 
solution. 

J  J.  prakt.  Chem.,  xl,  50. 


TRIVALENT   VANADIUM. 


Ill 


saved,  the  rest  of  the  product  being  removed  by  lixiviation. 
The  crystals  were  repeatedly  washed  by  decantation  with  95 
per  cent  alcohol,  and  finally  with  ether,  and  dried  in  a 
vacuum-desiccator. 

In  the  analysis  of  the  product  the  carbon  and  nitrogen  were 
determined  by  combustion.  The  vanadium  was  estimated  by 
titration  with  iodine,  and  the  potassium  as  sulphate,  in  a  sepa- 
rate portion,  after  the  oxidation  of  the  vanadium  to  vanadic 
acid  and  its  removal  as  lead  vanadate.* 


V 

c 

N 
K 


Calculated  for 

K3V(CN)6. 

.  15.74 
.  22.22 
.  25.93 
.  36.11 
100.00 


Pound. 

15.89 
21.80 
26.36 
36.47 
100.52 


This  salt  forms  another  member  of  the  series  of  complex 
cyanides  of  the  formula  K3M(CN)6,  of  which  the  other  mem- 
bers as  yet  known  are  K8Cr(CN)6,  K8Mn(CN)6,  K8Fe(CN)6, 
K3Co(CN)6,  K8Rh(CN)6,  and  K3Ir(CN)6.  The  crystals  ob- 
tained were  about  a  millimeter  in  length,  and  of  a  bright 
scarlet  color.  Owing  to  their  instability,  it  was  impossible 
to  measure  them,  and  thus  determine  whether  they  were 
isomorphous  with  the  other  members  of  the  series.  They 
appeared  under  the  microscope  to  be  rhombic  plates,  with 
well-formed  domes  and  base ;  in  polarized  light,  however,  they 
showed  inclined  extinction,  and  are  therefore  probably  mono- 
clinic  like  the  others.  In  potassium  ferricyanide  the  angle 
0  is  90°  6'. 

Potassium  vanadicyanide  is  readily  soluble  in  water,  in- 
soluble in  alcohol.  Its  aqueous  solution  grows  turbid  within 
a  few  minutes,  however,  but  is  much  more  stable  when  con- 
taining some  free  potassium  cyanide.  Even  in  that  case  it 
cannot  be  kept  for  any  length  of  time.  The  freshly-prepared 
solution  is  at  once  decomposed  by  acids,  turning  green.  It 


*  Roscoe  :  Ann.  Chera.  (Liebig),  Suppl.,  viii,  102. 


112  ON  SOME   COMPOUNDS  OF 

gives  off  a  slight  odor  of  hydrocyanic  acid,  as  does  the  solid 
salt  itself.  The  solution  is  at  first  stable  toward  alkalies  in 
the  cold,  but  on  heating  or  standing  for  some  time  the  hy- 
droxide separates  out. 

The  solution  yields  colored  precipitates  with  the  neutral 
solutions  of  various  metals,  of  which  the  following  are  the 
most  distinct : 

Ferrous  iron   ....  red-brown. 

Cadmium yellow. 

Copper yellow. 

Nickel purple. 

Manganese      ....  greenish-yellow. 

Silver  and  mercury  salts  are  reduced  by  it,  with  deposition 
of  the  metals.  None  of  these  precipitates  is  stable  toward 
acids,  and  their  color  soon  undergoes  a  change  on  standing. 

We  have  made  repeated  attempts  to  isolate  the  purple  pre- 
cipitate which  separates  on  the  first  addition  of  potassium 
cyanide  to  the  vanadic  solution,  but  without  success.  The 
compound,  probably  vanadic  cyanide,  is  extremely  unstable, 
and  on  drying  yields  a  green  or  brown  amorphous  product, 
which  is  obviously  a  mixture. 

The  vanadicyanides  of  ammonium  and  sodium  seem  to  exist 
only  in  solution.  Vanadium  cyanide  dissolves  in  excess  of 
ammonium  cyanide  or  sodium  cyanide,  to  solutions  of  the 
same  color  as  that  of  the  potassium  salt.  No  crystalline 
products,  however,  could  be  obtained  from  either  solution, 
either  by  evaporation  or  precipitation  with  alcohol.  When 
the  latter  is  employed,  the  compounds  decompose  at  once, 
with  separation  of  a  thick  blue  paste. 

The  properties  and  reactions  of  potassium  vanadicyanide 
are  of  special  interest  in  view  of  the  relative  stability  of  the 
complex  cyanides  of  the  other  metals  of  the  group.  The  only 
stable  compounds  of  trivalent  cobalt  are  those  which  contain 
the  metal  as  a  constituent  of  a  complex  radical,  either  posi- 
tive, as  in  the  cobaltiamines,  or  negative,  as  in  K3Co(CN)6, 
H3Co(CN)6,  etc.  The  corresponding  ferric  compounds,  in 


TRIVALENT   VANADIUM. 


113 


comparison  with  other  ferric  salts,  are  somewhat  less  stable 
than  the  cobaltic  compounds  as  compared  with  simple  cobaltic 
salts.  Thus,  for  example,  potassium  ferricyanide  is  less 
stable,  compared  with  ferric  sulphate,  than  is  potassium 
cobalticyanide,  when  compared  with  cobaltic  sulphate.  The 
complex  manganese  derivatives  are  relatively  still  less  stable. 
Among  the  latter  is  a  sodium  salt,  Na8Mn(CN)6,  but  the  free 
acid  is  unknown.  Chromic  cyanide  yields  neither  an  acid, 
H3Cr(CN)6,  nor  a  sodium  salt,  and  ammonium  chromicyanide  * 
is  very  unstable.  The  chromicyanide  solutions,  however, 
are  stable  towards  alkalies  even  on  boiling.  In  the  case  of 
vanadium,  neither  the  sodium  nor  ammonium  salts  can  be 
obtained;  potassium  vanadicyanide  is  instantly  decomposed 
by  acids,  with  evolution  of  hydrocyanic  acid,  and  is  stable 
towards  alkalies  only  in  the  cold.  The  simple  vanadic  salts 
are  comparatively  stable.  Aluminium,  which  has  the  lowest 
atomic  weight  of  all  the  metals  in  the  group,  is  precipitated 
as  hydroxide  when  potassium  cyanide  is  added  to  its  solution, 
and  no  cyanogen  compounds  at  all  of  this  metal  can  be  ob- 
tained. The  tendency  to  form  complex  radicals,  throughout 
the  entire  group,  as  compared  with  the  tendency  to  form 
simple  salts,  is  thus  seen  steadily  to  diminish  with  a  decrease 
in  the  atomic  weights  of  its  members. 

Potassium  Vanadisulphoeyanate,  K^V^ONS)^HtO.  — 
Among  the  characteristic  compounds  of  trivalent  chromium 
the  derivatives  of  chromic  sulphocyanate  are  very  prominent. 
Potassium  chromisulphocyanate,  K3Cr(CNS)«.6H2O,  is  almost 
as  stable  as  the  chromicyanide.  It  is  not  decomposed  by 
either  alkalies  or  acids  in  cold  solution,  f  A  number  of  other 
salts,  such  as  Ag3Cr(CNS)6,  Ba3[Cr(CNS)6]2,  etc.,  derivatives 
of  the  same  acid,  H3Cr(CNS)6,  are  also  known. 

We  have  succeeded  in  preparing  a  compound  of  vanadium 
analogous  to  this  potassium  salt,  and  find  that  it  corresponds 
very  closely  to  the  latter  in  its  reactions.  The  method  em- 
ployed was  as  follows : 

An  alcoholic    solution   of    potassium    sulphocyanate   was 


*  Ann.  Chera.  (Liebig),  iii,  163. 


t  Rosier:  Ibid.,  cxli,  185. 


8 


114  ON  SOME   COMPOUNDS  OF 

made  by  fusing  sulphur  with  potassium  cyanide,*  digesting 
the  product  with  absolute  alcohol,  and  filtering.  To  this 
solution  was  added  somewhat  less  than  the  calculated  quan- 
tity of  vanadium  chloride,  dissolved  in  a  small  volume  of 
water.  A  precipitate  of  potassium  chloride  at  once  appeared, 
and  the  solution  assumed  a  deep  brown  color.  After  digestion 
for  an  hour  on  the  water-bath,  the  solution  was  concen- 
trated by  evaporation,  and  then  placed  in  a  vacuum-desicca- 
tor to  crystallize.  The  first  crop  of  crystals  consisted  of  a 
mixture  of  about  equal  proportions  of  potassium  sulphocy- 
anate  and  vanadisulphocyanate.  This  was  removed,  and  the 
evaporation  continued  until  the  solution  was  of  a  thick,  syrupy 
consistency.  A  large  quantity  of  homogeneous,  dark-red  crys- 
tals, almost  black,  were  thus  obtained.  They  were  cleaned 
as  thoroughly  as  possible  by  pressure  between  filter  paper, 
washed  with  ether,  and  dried  in  a  vacuum.  The  analysis 
gave  the  following  results : 

Calculated  for  w/.     ^ 

K3V(CNS)6.4H20. 

K 19.90  19.52 

C 12.24 

N 14.29  14.73 

S 32.65  33.23 

V 8.68                     8.55,  8.22,  8.79 

H20    .    .     .    .  12.24  13.09 
100.00 

Potassium  vanadisulphocyanate,  like  the  corresponding 
chromium  salt,  is  extremely  soluble  in  both  alcohol  and  water, 
but  is  stable  only  in  presence  of  an  excess  of  potassium  sul- 
phocyanate.  The  pure  salt  is  decomposed  by  either  solvent, 
forming  a  green  solution.  Crystals  mixed  with  a  small  quan- 
tity of  sulphocyanate  are  very  hygroscopic,  dissolving  in  the 
water  absorbed.  Toward  oxygen  the  salt  is  the  most  stable 
of  any  which  we,  have  prepared.  The  vanadium  in  the  radi- 
cal V(CNS)6  undergoes  oxidation  only  very  slowly,  and  in 

*  Chem.  Zeitung,  1866,  666. 


TRIVALENT  VANADIUM. 


115 


presence  of  potassium  sulphocyanate  the  solution  may  be  left 
exposed  to  the  air  for  some  time  without  losing  its  charac- 
teristic dark-brown  color.  Alkalies  precipitate  vanadic  hy- 
droxide from  the  solution  only  on  boiling,  but  it  is  at  once 
decomposed  by  acids. 

The  preparation  of  corresponding  salts  of  other  metals,  such 
as  Na3V(CNS)6,  Ba8[V(CNS)6]2,  etc.,  we  have  not  yet 
attempted,  but  we  hope  to  do  so  in  the  near  future.  Our  in- 
vestigations on  the  vanadic  compounds  in  general  will  be 
continued. 

NEW  HAVEN,  May,  1898. 


ON  AN  ISOMER  OF   POTASSIUM  FERRICYANIDE.* 

BY  JAMES  LOCKE  AND  GASTON  H.  EDWARDS. 

THE  behavior  of  potassium  ferricyanide  toward  powerful 
oxidizing  agents  has  been  virtually  but  once  the  subject  of 
investigation.  In  1869  Stadeler,f  in  support  of  his  theory 
that  the  iron  in  sodium  nitroprussiate,  Na2Fe(CN)5NO2,  is 
tetravalent,  sought  to  obtain  the  related  perferricyanide, 
K2Fe(CN)6,  by  the  action  of  iodine  upon  the  ferricyanide. 
He  thus  obtained  a  greenish-brown,  crystalline  product,  which 
was  apparently  too  impure  for  analysis,  for  he  assigned  the 
above  formula  to  it  without  having  quantitative  data  upon 
which  to  base  his  conclusions.  A  body  having  approximately 
the  same  characteristics  as  Stadeler's  compound  was  after- 
ward obtained  by  Bong,!  by  the  action  of  potassium  chlorate 
and  sulphuric  acid  upon  the  ferricyanide.  To  this  product 
was  likewise  assigned  the  formula  K2Fe(CN)6,  but  it  could  be 
prepared  only  in  admixture  with  a  large  percentage  of  potas- 
sium sulphate,  and  no  analysis  of  it  was  made.  The  principal 
work  upon  the  subject,  and  the  only  work  in  which  analytical 
results  were  obtained,  was  performed  by  Skraup  in  1877. 
The  latter,  to  a  certain  extent,  adopted  Bong's  method,  but 
he  substituted  hydrochloric  acid  for  sulphuric,  and  isolated 
his  reaction-product  by  repeatedly  precipitating  the  aqueous 
solution  with  alcohol.  He  finally  obtained  a  completely 
amorphous,  black  or  dark-violet  powder,  which  was  intensely 
hygroscopic  and  smelled  strongly  of  cyanogen.  This  body 
Skraup  submitted  to  thorough  analysis,  but  he  was  unable 
to  obtain  satisfactory  results.  The  percentage  of  cyanogen 
fell  much  below  the  amount  calculated  for  the  compound 

*  Amer.  Chem.  Jour.,  xxi,  March,  1899. 

t  Ann.  Chem.  (Liebig),  cli,  1. 

J  Bull.  Soc.  Chim.  (1875),  xxiv,  26& 


AN  ISOMER   OF  POTASSIUM  FERPJCYANIDE.       117 

K2Fe(CN)6  (about  4.0  per  cent).  But  the  iron  and  potassium, 
while  correspondingly  high,  were  present  in  the  approximate 
ratio  of  one  to  two,  and  he  therefore  assumed  the  body 
possessed  the  formula  previously  suggested  by  Stadeler  and 
Bong. 

The  details  of  the  method  of  preparation  used  by  Skraup 
were  briefly  as  follows :  Assuming  the  reaction  to  proceed  in 
the  simplest  manner,  viz.,  according  to  the  equation, 

6K3Fe(CN)6  +  KC103  +  6HC1  =  6K2Fe(CN)6  +  7KC1  +  3H20, 

he  added  to  the  hot  solution  of  50  g.  potassium  ferricyanide 
and  4  g.  of  potassium  chlorate,  in  100  c.  c.  water,  the  cal- 
culated quantity  of  hydrochloric  acid  (4  g.,  sp.  gr.  1.19)  in 
about  75  c.  c.  water.  The  solution  quickly  assumed  a  pecu- 
liar red  color,  and  after  a  few  minutes  effervescence  was 
observed,  presumably  escaping  cyanogen  chloride.  Shortly 
afterwards  the  solution  was  cooled  down  and  allowed  to 
stand  for  twenty-four  hours.  Precipitation  with  alcohol  then 
yielded  a  crystalline  product,  which  was  redissolved  in  water 
and  reprecipitated  with  alcohol  about  twelve  tunes.  On 
the  third  or  fourth  repetition  of  this  operation  the  body 
began  to  lose  its  crystalline  nature,  and  the  final  product, 
which  he  used  for  his  analyses,  was  completely  amorphous. 
The  most  characteristic  reaction  of  the  new  compound,  and 
the  only  one  which  indicated  that  its  iron  was  in  the  tetra- 
valent  state,  was  found  to  be  its  decomposition  by  alkalies. 
On  being  boiled  with  the  latter  it  yielded  ferric  hydroxide, 
potassium  ferrocyanide,  and  potassium  cyanate. 

The  method  employed  by  Skraup  is  open  to  criticism  at  two 
points.  If  the  reaction  proceeds  as  he  supposed,  it  should  be 
stopped  before  the  evolution  of  cyanogen  chloride  begins,  for 
this  must  be  due  to  the  decomposition  of  the  substance.  In 
describing  the  reactions  of  the  salt,  Skraup  states  that  it  is 
slowly  decomposed  by  alcohol.  It  would  hardly  seem  advisa- 
ble, therefore,  to  employ  repeated  precipitation  with  alcohol 
as  a  means  of  purifying  it.  These  considerations  led  us  to 
believe  that  the  final,  amorphous  body  was  simply  a  decompo- 


118  ON  AN  ISOMER   OF 

sition-product  of  the  supposedly  impure  crystalline  precipitate 
obtained  on  the  first  addition  of  alcohol  to  the  oxidized  solu- 
tion, and  that  this  body  might  perhaps  be  obtained  in  a  state 
more  suitable  for  analysis  by  some  other  supplementary 
process. 

We  therefore  prepared  this  salt  according  to  Skraup's 
directions,  but  placed  the  mixture  in  ice-water  as  soon  as  the 
first  sign  of  effervescence  was  observed.  The  time  required 
for  the  reaction  varies  greatly  with  the  temperature.  When 
the  hydrochloric  acid  is  added  to  the  boiling  solution,  the  gas 
comes  off  at  once,  but  at  95°,  the  temperature  at  which  we 
worked,  about  five  minutes  are  required.  When  the  solution 
had  cooled  to  almost  20°,  it  was  filtered,  and  slightly  less  than 
an  equal  volume  of  alcohol,  or  just  enough  to  bring  about 
incipient  precipitation,  was  added.  The  solution  was  then 
allowed  to  stand  until  its  temperature  had  fallen  nearly  to  0°. 
A  dense  crystalline  precipitate  separated  out,  from  which  the 
mother-liquid  was  drawn  off  as  completely  as  possible,  without 
washing,  on  a  suction  filter.  The  product  was  then  redissolved 
in  as  little  water  as  possible,  and  partially  reprecipitated  with 
a  much  smaller  volume  of  alcohol.  On  a  second  repetition  of 
this  operation,  the  crystalline  nature  of  the  precipitate  became 
less  distinct,  as  Skraup  also  observed.  The  purification  was 
therefore  carried  no  further.  The  salt  was  extremely  soluble 
in  water,  yielding  a  solution  which  was  green  by  reflected 
light,  and  by  transmitted  light  had  a  peculiar  reddish  tint. 
Thus  far  it  corresponded  with  Skraup's  observations,  but  on 
boiling  with  ammonium  hydroxide  it  gave  only  a  trace  of 
ferric  hydroxide  and  potassium  ferrocyanide,*  indicating  that 
our  supposition  was  correct,  that  Skraup's  body  was  a  product 
of  decomposition  of  his  first  precipitate. 

The  salt  obtained  on  the  third  precipitation  with  alcohol 
(the  yield  was  about  1  g.)  was  carefully  examined  under 
the  miscroscope  for  impurities.  It  consisted  of  very  small, 

*  A  quantitative  determination  of  the  ferrocyanide  thus  formed  by 
titration  with  potassium  *permanganate,  showed  that  only  0.07  per  cent  of 
the  salt  had  undergone  reduction. 


POTASSIUM  FERRICYANIDE. 


119 


greenish-yellow  needles,  among  which  no  foreign  ingredients 
could  be  seen.  The  body  was,  therefore,  subjected  to  analy- 
sis, in  the  expectation  that  it  would  give  results  correspond- 
ing closely  with  the  formula  K2Fe(CN)6.  To  our  surprise, 
however,  we  found  that,  together  with  11.83  per  cent  of 
water,  it  contained  the  four  elements  in  the  same  ratio  as 
potassium  ferricyanide  itself,  corresponding  almost  exactly 
with  the  formula  K3Fe(CN)6.  The  results  of  this  first  analy- 
sis (I)  follow : 


H20   .    . 
Fe.    .    . 

Calculated  for 
K3Fe(CN)6  with 
11.83  per  cent  H2O 

.    .     11.83 
.    .    15.01 

Found. 

11.83 
15.43 
19.20 

22.70 
31.60 

Ratio. 

0.344 
1.97 
2.07 
1.0 

1.03 
5.91 
6.21 
3.0 

C   .     .    . 

.    .     19.30 

N  .    .    . 

.    .     22.51 

K  .    .    . 

.     .    31.35 

100.00 


100.76 


The  water  present  we  afterwards  found  to  be  due  chiefly  to 
the  extreme  difficulty  with  which  the  salt  can  be  dried.  On 
precipitation  the  latter  comes  down  as  a  network  of  very  fine, 
delicate  needles,  in  the  capillary  spaces  between  which  the 
water  is  most  obstinately  retained.  By  allowing  the  salt  to 
stand  for  several  days  in  a  vacuum  over  sulphuric  acid,  the 
percentage  of  water  can  be  reduced  until  it  corresponds  with 
the  value  calculated  for  the  formula  K3Fe(CN)6+H2O.*  Our 
first  supposition  was  that  the  presence  of  this  water  was  the 
cause  of  the  difference  between  the  new  compound  and  the 
normal  ferricyanide,  or,  in  other  words,  that  it  was  water  of 
constitution.  This  hypothesis,  however,  is  inadmissible ;  for 
the  corresponding  silver  salt,  which  can  readily  be  obtained,  is 
like  normal  silver  ferricyanide,  —  an  anhydrous  compound,  and 
has  the  formula  Ag3Fe(CN)6.  The  salt  must,  therefore,  be 
regarded  as  an  actual  isomer  of  potassium  ferricyanide.*  What 
the  structural  difference  between  the  two  is,  or  how  the  isomer 
happens  to  be  formed  through  the  action  of  such  a  substance 

*  Found,  5.55  per  cent.    The  theory  requires  5.18  per  cent. 


120  ON  AN  ISOMER   OF 

as  chloric  acid,  we  cannot  explain.  But  repeated  analyses  of 
the  compound  itself,  and  also  of  the  silver  salt,  together  with 
the  quantitative  study  of  reactions  in  which  it  was  completely 
converted  into  the  normal  ferricyanide,  leave  no  doubt  as  to 
its  composition.  Its  reactions,  on  the  other  hand,  are  in  some 
cases  totally  different  from  those  of  the  latter  compound.  We 
propose  for  it,  as  a  temporary  designation,  the  term  potassium 
yQ-ferricyanide. 

The  various  analyses  of  the  isomer  published  below  were 
made  from  as  many  different  preparations  obtained  under  as 
varied  conditions  as  possible.  In  the  course  of  the  work  it 
was  found  that  two  precipitations  with  alcohol  are  sufficient 
to  yield  the  body  in  a  state  pure  enough  for  analysis.  Even 
on  the  first  precipitation  it  is  nearly  pure,  giving  no  ferric 
hydroxide  when  boiled  with  ammonia  and  containing  only  a 
trace  (about  0.5  per  cent)  of  chlorine.  By  using  somewhat 
less  than  an  equal  volume  of  alcohol  on  the  second  precipita- 
tion, a  yield  of  about  15  g.  could  be  obtained,  and  when 
the  conditions  were  very  carefully  observed  the  individual 
crystals  were  large  enough  to  be  observed  by  the  naked  eye. 
A  slight  variation  of  the  conditions  in  any  particular,  how- 
ever, leads  to  the  formation  simply  of  a  crystalline  paste, 
which  it  is  almost  impossible  to  purify.  The  properly  pre- 
pared salt  can  be  easily  and  thoroughly  washed  with  75  per 
cent  alcohol;  when  placed  in  a  vacuum,  after  subsequent 
washing  with  absolute  alcohol,  it  falls  to  an  extremely  light, 
voluminous  powder.  This  possesses  a  pure,  rich  olive  color, 
which  appears  brown  when  observed  by  gaslight.  It  dis- 
solves with  the  utmost  ease  in  water,  but,  unlike  Skraup's 
compound,  it  is  not  noticeably  hygroscopic.  The  solution  is 
comparatively  stable,  though  it  undergoes  gradual  decompo- 
sition on  standing.  This  decomposition  is  not  accompanied 
by  the  formation  of  either  potassium  cyanide,  hydrocyanic 
acid,  or  free  cyanogen,  nor  does  the  dry  salt  possess  the 
slightest  odor  of  the  latter  substance. 

Various  attempts  were  made  to  obtain  the  salt  in  the  form 
of  larger  crystals,  by  the  evaporation  of  its  concentrated 


POTASSIUM  FERRICYAN1DE. 


121 


aqueous  solution.  But  owing  to  the  capillary  action  of  the 
needles  as  they  separated  on  the  sides  of  the  vessel,  only  a 
dense  efflorescent  growth  was  obtained,  from  which  no  indi- 
vidual crystals  could  be  isolated.  Analysis  II  below  is  from 
one  of  these  crops.  When  a  small  quantity  of  the  salt  is  dis- 
solved in  a  drop  or  two  of  water  and  allowed  to  crystallize  out 
on  an  object  glass,  it  is  obtained  as  an  intimate  network  of 
microscopic  needles,  of  characteristic,  very  slightly  tapering 
form.  They  are  probably  rhombic,  showing  parallel  extinc- 
tion and  slightly  pleochroic.  Among  them  no  trace  of  the 
heavy  prismatic  or  block-shaped  crystals  of  the  normal  or 
a-ferricyanide  could  be  detected.  In  crsytallization  experi- 
ments with  mixtures  of  the  two  isomers,  on  the  other  hand, 
they  could  be  distinguished  at  a  glance,  showing  that  the  new 
compound  is  not  merely  the  a-fenicyanide  in  a  new  crystallo- 
graphic  modification. 

Analytical  Results.  —  For  the  determination  of  potassium 
and  iron  the  compound  was  decomposed  by  heating  with  con- 
centrated nitric  acid.  The  iron  was  then  precipitated  with 
ammonium  hydroxide,  and  the  potassium  weighed  as  chloride 
or  sulphate.  The  nitrogen  was  determined  by  combustion. 
The  total  combustion  of  the  carbon  takes  place  with  great 
difficulty,  and  the  results  for  that  element  were  rather  low 
(one  per  cent  or  more).  In  view  of  the  above  determination, 
(I)  however,  together  with  experiments  on  the  quantitative 
conversion  of  the  compound  into  potassium  a-ferricyanide,  its 
further  determination  was  deemed  unnecessary,  and  the  per- 
centage of  cyanogen  was  calculated  from  that  of  the  nitrogen. 
The  water  was  determined  by  combustion. 


ii. 


in. 


CN 

Fe  . 
K  . 
H20 


Found. 
Per  cent. 

45.31 

16.95 

33.91 

5.41 

101.47 


Ratio. 

6.00 
1.04 
3.00 
1.00 


Pound. 
Per  cent. 

45.13 

16.02 

32.90 

4.65 

98.70 


Ratio. 

6.15 
1.01 
3.00 
0.8 


122  ON  AN  ISOMER   OF 

IV. 


Ratio  Average  of  tho         Calculated  for 

3  Analyses.  K3Fe(CN)6.H2O. 

CN    .     .    45.05  5.94 

Fe      .    .     16.98  1.05 

K  .     .     .     34.11  3.00 

H20   .     .       4.73  0.87 
100.87 

A  subsequent  determination  of  water,  according  to  the 
method  of  Jannasch  and  Locke,*  in  another  preparation  which 
had  previously  been  allowed  to  stand  in  a  vacuum  over  sul- 
phuric acid  for  three  days,  gave  5.55  per  cent.  There  seems 
to  be  no  doubt,  therefore,  that  the  body  possesses  the  formula 
K8Fe(CN)6.H2O.  In  order  to  prove  this  definitely,  however, 
and  at  the  same  time  make  a  direct  estimation  of  the  cy- 
anogen, a  method  was  sought  by  which  the  body  could  be 
quantitatively  converted  to  the  a-ferricyanide.  Preliminary 
experiments  showed  that  it  passed  into  potassium  ferrocyanide 
upon  reduction,  but  its  titration  on  that  principle,  either  ac- 
cording to  the  method  of  Mohr  f  or  after  reduction  with  ferrous 
hydroxide,  gave  no  satisfactory  results.  The  most  conven- 
ient means  of  reduction  we  found  to  be  sodium  amalgam  in 
alkaline  solution.  This  converted  the  substance  completely 
into  the  ferrocyanide,  without  the  separation  even  of  traces  of 
iron.  The  ferrocyanide  was  then  titrated  with  potassium 
permanganate  in  sulphuric  acid  solution.  The  details  of  the 
method  were  first  worked  out  with  potassium  a-ferricyanide, 
and  the  best  conditions  found  to  be  as  follows  :  The  solution 
of  the  salt  (about  0.2  g.)  in  100  c.  c.  of  water,  was  rendered 
slightly  alkaline  with  sodium  carbonate,  and  a  piece  of  5  per 
cent  sodium  amalgam  was  then  added.  During  the  reduc- 
tion the  solution  was  kept  on  the  steam-bath.  In  the  course 
of  an  hour  or  so  the  mercury  was  filtered  off  and  the  solution 
cooled  and  very  slightly  acidified  with  sulphuric  acid.  It  was 
then  titrated  with  a  solution  of  permanganate  until  the  red 
color  of  the  latter  remained  for  half  a  minute  or  more. 

*  Zeitschr.  anorg.  Chem.,  vi,  174.  f  Ann.  Chem.  (Liebig),  cv,  62. 


POTASSIUM  FERRIC YANIDE. 


123 


With  potassium  a-ferricyanide  the  following  results  were 
obtained : 

1  c.  c.  KMnO4  solution  =  0.00572  g.  Fe  =  0.0336  g. 
K8Fe(CN)6. 


I  . 

II  . 

Ill  . 


K8Fe(CN)e 
taken. 

0.2596 
0.2402 
0.1926 


C.  c.  KMnO4  solu-      C.  c.  KMnO4 
tion  used.  calculated. 


7.65 
7.10 
5.70 


7.72 
7.15 
5.71 


The  same  method  of  procedure  gave  for  the  new  compound 
the  following  results : 


I 

II 

III 

IV 

V 

VI 


taken. 

0.1611 
0.2520 
0.1946 
0.2641 
0.1427 
0.2208 


C.  c.  KMnO4  solu-    C.  c.  KMnO4  solu- 
tion used.  tion  calculated. 


4.55 
7.20 
5.40 
7.35 
4.10 
6.30 


4.55 
7.11 
5.49 
7.45 
4.04 
6.26 


In  order  to  make  sure  that  in  these  experiments  only  potas- 
sium a-ferricyanide  remained  in  the  solutions,  or,  in  other 
words,  that  the  conversion  of  the  /?-ferricyanide  to  the  latter 
compound  was  absolutely  quantitative,  the  amount  of 
a-ferricyanide  which  the  solutions  in  V  or  VI  contained  was 
gravimetrically  determined.  This  was  accomplished  by  pre- 
cipitating the  titrated  solutions  with  silver  nitrate,  and  esti- 
mating the  percentage  from  the  silver,  which  was  weighed  as 
chloride.  The  results  were  very  exact,  the  amount  of  silver 
found  differing  by  little  more  than  a  milligram  from  that 
required  by  theory : 

V  Found,  0.1347  g.  Ag  =  0.1367  g.  K8Fe(CN)8. 

Calculated,  0.1332  g.  Ag  =  0.1352  g.  K8Fe(CN)(,. 
VI  Found,  0.2048  g.  Ag  =  0.2079  g.  K8Fe  (CN)e. 
Calculated,  0.2061  g.  Ag  =  0.2092  g.  K8Fe(CN)6. 


The  average  percentage  of  cyanogen  in  the  /3-ferricyanide, 


124 


ON  AN  ISOMER   OF 


as  calculated  from  these  six  determinations,  is   45.07.     The 
theory  requires  44.96  per  cent. 

Potassium  /3-ferricyanide,  like  the  normal  salt,  yields  char- 
acteristic precipitates  with  the  solutions  of  most  of  the  heavy 
metals.  These  have,  in  general,  the  same  characteristics  as 
the  corresponding  a-ferricyanides,  and  in  some  cases  pass  over 
into  the  latter  with  extreme  ease.  The  less  notable  of  these 
precipitates  are  collected  briefly  in  the  table  below,  in  which, 
for  the  sake  of  comparison,  the  a-ferricyanides  are  also 
included.  The  reactions  examined  were  brought  about  in  2 
per  cent  solutions.  In  the  case  of  silver,  bismuth,  stannic 
tin,  and  lead,  the  reactions  will  be  discussed  more  fully,  as 
they  present  characteristic  points  of  difference  between  the 
two  ferricyanic  groups. 


/3-Ferricyanides. 

Cd.  Dirty  green,  soluble  in 
(NH4)2C03,HC1,  insol- 
uble in  HN03. 

Cu.   Yellowish-green,    insolu- 
ble in  HN08  or  HC1. 
Fem.   Dark    yellow    coloration, 
blue  precipitate  on  boil- 
ing. 

Fen.   Blue  precipitate. 
Hgn.   No  precipitate. 

Co.  Dark  red  precipitate,  in- 
soluble in  HC1  or  HN03. 

Mn.  Brown  precipitate,  insol- 
uble in  NH4OH,  HC1, 
or  HN08. 

Hg1.  Yellowish-green,  floccu- 
lent  precipitate.  Rap- 
idly undergoes  re- 
duction on  boiling, 
becoming  blue. 

!Ni.  Dark  yellowish-green,  in- 
soluble in  HNO,  or  HC1. 

Zn.  Yellowish-green,  soluble 
in  HC1,  (NH4)2C03,  in- 
soluble in  HNO». 


a-Ferricyanides. 

Pale  yellow,  soluble  in 
(NH4)2C03,HC1,  insol- 
uble in  HN03. 

Dark  greenish-yellow,  in- 
soluble in  HN03  or  HC1. 

Dark  red  coloration,  blue 
precipitate  on  boiling. 

Blue  precipitate. 
No  precipitate. 
The  same. 

The  same. 


Pale  yellow,  undergoes 
reduction  only  slowly 
on  boiling. 


Light  yellow,  same  be- 
havior. 
Yellow,  same  behavior. 


POTASSIUM  FERRICYANIDE.  125 

The  /3-ferricyanides  of  these  metals,  as  is  seen,  resemble  the 
a-compounds  in  nearly  all  particulars,  being  distinguished 
from  them  chiefly  in  having  a  more  or  less  pronounced  green 
color.  It  might  be  supposed,  therefore,  that  they  are  identi- 
cal with  them,  but  colored  by  slight  impurities.  But  the  be- 
havior of  the  salts  of  bismuth,  stannic  tin,  lead,  and  silver 
shows  that  this  is  not  the  case.  Bismuth  a-ferricyanide  is  a 
very  sparingly  soluble,  straw-colored  precipitate,  which  is  de- 
posited even  from  very  dilute  solutions  of  potassium  ferricy- 
anide  on  addition  of  bismuth  nitrate.  It  is  likewise  insoluble 
in  concentrated  nitric  acid.  A  solution  of  potassium  p-ferricy- 
anide,  on  the  other  hand,  when  freshly  prepared,  gives  no  trace 
of  a  precipitate  with  bismuth  nitrate.  The  solution  assumes 
a  slightly  greenish  tint,  but  even  when  concentrated  remains 
otherwise  unaltered  for  some  tune.  On  standing,  and  espe- 
cially when  exposed  to  the  action  of  the  direct  sunlight,  it 
deposits  large  granules  of  a  black,  crystalline  compound, 
which  we  have  not  yet  fully  examined,  but  which  is  appar- 
ently bismuth  ferrocyanide. 

Stannic  chloride,  on  the  other  hand,  yields  no  precipitate 
with  potassium  a-ferricyanide,  but  precipitates  the  isomer 
completely.  The  resulting  compound  comes  down  as  a  slimy, 
pure  green  body,  which  is  insoluble  in  either  hydrochloric  or 
nitric  acid.  We  have,  however,  been  unable  to  obtain  it  in  a 
state  suitable  for  analysis. 

A  comparative  study  of  the  lead  salts  was  kindly  under- 
taken by  Mr.  H.  A.  North.  While  lead  ferricyanide  is  not 
precipitated  by  potassium  a-ferricyanide,  under  ordinary  cir- 
cumstances, it  is  much  less  soluble  in  water  than  either  the 
latter  compound  or  lead  nitrate.  When  concentrated  solu- 
tions of  the  two  are  mixed  in  the  proper  proportions,  it  slowly 
separates  out  in  large,  dark-red  crystals.*  Mr.  North  made 
this  salt  by  dissolving  the  calculated  quantities,  or  3  g. 
each,  of  potassium  ferricyanide  and  lead  nitrate  in  7  c.  c.  and 
8  c.  c.  of  water,  respectively.  On  allowing  the  mixed  solutions 
to  stand  for  a  few  minutes,  he  obtained  more  than  a  gram  of 
*  Rammelsberg,  J.  prakt.  Chem.  (2),  xxxix,  455. 


126  ON  AN  ISOMER   OF 

well-crystallized  lead  ferricyanide.  A  similar  experiment  was 
then  made,  with  exactly  the  same  quantities,  potassium 
/3-ferricyanide  being  used  instead  of  the  a-salt.  No  crystalli- 
zation took  place,  indicating  that  lead  y3-ferricyanide  is  much 
more  soluble  in  water  than  its  isomer.  This  solution  was 
allowed  to  stand  over  night,  and  by  morning,  in  addition  to 
an  efflorescent  product,  more  or  less  of  the  normal  lead  o-ferri- 
cyanide  had  crystallized  out,  the  /3-ferricyanide  having  partially 
passed  over  into  the  latter  compound.  The  solution  then  gave 
the  usual  straw-colored  precipitate  with  bismuth  nitrate,  with 
which  it  had  not  reacted  twelve  hours  before. 

Various  attempts  were  made  to  isolate  the  /3-lead  salt  by 
other  means,  but  without  much  success.  The  most  satisfac- 
tory results  were  obtained  by  dissolving  lead  oxide  in  glacial 
acetic  acid,  and  adding  to  the  solution  the  calculated  quantity 
of  potassium  /3-ferricyanide,  dissolved  in  25  c.  c.  of  glacial  acetic 
acid  and  7  c.  c.  of  water.  A  green,  amorphous  precipitate 
separated  out,  which  was  readily  soluble  in  water  forming  a 
greenish-red  solution,  and  this  yielded  no  precipitate  with 
bismuth  nitrate.  An  analysis  of  the  product  showed  that  it 
contained  49  per  cent  lead,  and  no  potassium,  but  no  simple 
atomic  ratio  was  evident  between  the  lead  and  nitrogen, 
which  was  somewhat  low.  It  is  probable,  therefore,  that  the 
body  was  a  mixture.  An  experiment  made  with  potassium 
a-ferricyanide,  in  a  similar  manner,  yielded  a  crystalline  pre- 
cipitate of  the  ordinary  lead  ferricyanide. 

The  most  interesting  /3-ferricyanide  of  a  heavy  metal  which 
we  have  obtained  is  the  silver  salt.  This  is  thrown  down 
quantitatively  as  a  dark  brown,  flocculent  precipitate,  which 
can  be  readily  filtered  and  washed.*  Its  most  marked  charac- 
teristic is  the  ease  with  which  it  passes  into  the  a-ferricyanide. 
This  takes  place  simply  when  the  precipitate,  suspended  in  its 
mother-liquid,  is  heated  to  100°.  The  conversion  is  indicated 
by  the  change  in  color  to  the  bright  orange  of  the  a-ferricy- 
anide. The  silver  salt  was  prepared  for  analysis  by  adding  the 
potassium  salt  to  a  slight  excess  of  silver  nitrate,  both  being  in 

*  On  drying  it  forms  a  light,  brown  powder. 


POTASSIUM  FERRICYANIDE. 


127 


Calculated  for 

Ag,Fe(CN)8. 

60.47 

Found. 
I.               II. 

59.41    60.00 

10.45 

10.84     .  .  . 

15.67 

15.31 

ice-cold  solution.  The  precipitate  was  washed  with  ice-water, 
then  with  alcohol,  and  finally  with  ether,  to  secure  rapid  dry- 
ing, and  then  allowed  to  stand  in  a  vacuum,  without  exposure 
to  light.  The  results  of  the  analyses  were  as  follows : 


Ag 
Ee 

N 


The  readiness  with  which  the  silver  salt  passes  into  silver 
a-f erricyanide  presented  another  means  of  ascertaining  whether 
the  conversion  of  the  one  ferricyanic  group  into  the  other  is 
actually  quantitative.  Weighed  quantities  of  the  potassium 
salt  were  precipitated  with  silver  nitrate  in  the  cold,  and  one 
of  the  precipitates  (I)  then  rapidly  heated  in  its  mother-liquid 
until  it  had  assumed  the  orange-red  color  of  silver  a-ferricy- 
anide.  The  silver  in  each  of  the  precipitates  was  then  deter- 
mined, and  found  to  be  as  calculated  for  the  compound 
Ag3Fe(CN)6. 

I  0.2912  g.  K3Fe(CN)6.H20  gave  0.2729  g.  Ag. 

calculated  0.2724  g.  Ag. 
II  0.2470  g.          "        "         gave  0.2291  g.  Ag. 

calculated  0.2307  g.  Ag. 

The  filtrates  were  then  very  thoroughly  examined  for  prod- 
ucts other  than  potassium  nitrate.  The  filtrate  from  (I)  con- 
tained a  trace  of  iron,  which  was  precipitated  and  weighed. 
It  amounted  only  to  0.15  per  cent  of  the  potassium  salt.  In 
neither  filtrate  could  either  hydrocyanic  or  cyanic  acid  be  de- 
tected. The  change  which  the  silver  salt  undergoes  on  heat- 
ing must  therefore  be  assumed  to  take  place  without  the 
formation  of  any  substance  other  than  silver  a-ferricyanide, 
and  to  consist  simply  in  a  rearrangement  of  atoms  in  the  mole- 
cule Ag3Fe(CN)6. 

It  was  hoped  that  by  acting  on  the  silver  salt  with  the  cal- 
culated quantity  of  hydrochloric  acid  the  free  /3-ferricyanic 
acid  could  be  prepared.  The  solution  obtained  gave  for  the 


128  ON  AN  I  SOME  R   OF 

moment  no  precipitate  with  bismuth  nitrate,  showing  that  the 
/3-acid  had  been  formed,  but  the  latter  passed  within  a  few 
minutes  into  the  normal  acid,  and  then  into  further  decompo- 
sition-products. Efforts  to  prepare  the  salts  of  calcium  and 
barium  in  the  same  way  also  failed,  the  normal  ferricyanides 
being  finally  obtained. 

In  regard  to  the  constitution  of  the  /3-ferricyanic  group  we 
have  little  to  state.  Any  attempt  to  assign  a  definite  struc- 
tural formula  to  it  would,  for  the  present,  be  pure  speculation. 
The  suggestion  offers  itself  that  one  of  the  two  isomers  con- 
tains isonitril  groups,  the  other  nitril  groups.  But  this  view, 
at  least,  is  absolutely  refuted  by  the  identical  behavior  of  the 
two  on  reduction.  So  far  as  we  can  find,  there  are  no  cases 
known  where  isomers  containing  respectively  the  — CN  and 
— NC  groups  yield  the  same  product  with  nascent  hydrogen. 
On  the  other  hand,  if  both  ferricyanides  contain  only  cyano- 
gen groups,  the  /3-compound  becomes  of  especial  importance 
because  of  its  bearing  on  Werner's  theory.  According  to  the 
latter  the  ferricyanic  group  is  not  to  be  represented  by  the 
structural  formula,  but  simply  as  a  radical  in  which  the  cyano- 
gen groups  occupy  "  co-ordination  positions  "  about  the  ferric 
atom.  Isomerism  between  two  equivalent  Fe(CN)6  groups, 
if  this  is  so,  can  be  due  only  to  stereochemical  causes.  The 
greatest  value  of  Werner's  theory  lies  in  the  explanation 
which  it  offers  of  the  cases  of  isomerism  among  the  platin- 
amine  and  cobaltiamine  compounds.  The  six  co-ordinated 
groups  are  supposed  to  occupy  the  angles  of  a  regular  octa- 
hedron, in  the  centre  of  which  is  the  metal.  Isomerism  is 
then  possible  whenever  two  or  more  of  the  co-ordinated  groups 
differ  from  the  others.  But  according  to  it  a  radical  in  which 
they  are  all  alike,  such  as  Fem(CN)6,  cannot  have  two  differ- 
ent configurations,  or,  in  other  words,  exist  in  isomeric  modi- 
fications. It  would  seem,  therefore,  that  the  existence  of 
potassium  /3-ferricyanide  stands  in  direct  contradiction  to  such 
a  theory,  at  least  in  its  present  form. 

It  may  of  course  be  that  the  /3-ferricyanide  is  a  mixture 
of  two  substances  in  proportions  giving  the  atomic  ratio 


POTASSIUM  FERRICYANIDE.  129 

K3Fe(CN)6.  But  throughout  all  our  investigations  we  have 
searched  for,  and  failed  to  find,  a  single  indication  that  such 
is  the  fact.  Its  completely  crystalline  and  homogeneous  ap- 
pearance, the  constant  composition  of  different  products,  and 
all  its  observed  reactions  point  closely  to  its  being  an  indi- 
vidual chemical  compound.  Our  investigations  will  be  con- 
tinued, however,  and  we  hope  to  bring  more  light  to  bear 
upon  the  subject  within  a  short  time. 

NEW  HAVEN,  December  12, 1898. 


ON  THE  FORMATION  OF  POTASSIUM  /9-FERRI- 
CYANIDE  THROUGH  THE  ACTION  OF  ACIDS 
UPON  THE  NORMAL  FERRIC YANIDE.* 

BY  JAMES  LOCKE  AND  GASTON  H.  EDWAKDS. 

WE  have  shown  in  a  previous  paper  f  that  when  a  solution 
of  potassium  ferricyanide  is  heated  for  a  short  time  with 
potassium  chlorate  and  hydrochloric  acid,  an  isomer  of  this 
salt  is  obtained,  which  crystallizes  with  one  molecule  of  water. 
This  salt  had  already  been  obtained  by  Skraup  J  and  others, 
hi  an  impure  state,  by  the  action  of  oxidizing  agents,  and  was 
regarded  by  them  as  an  oxidation  product  of  the  normal  ferri- 
cyanide, with  the  formula  K2Fe(CN)6.  At  the  time  of  our 
first  investigation  we  likewise  ascribed  its  formation  to  the 
oxidizing  action  of  the  potassium  chlorate,  but  have  since 
found  that  it  is  due  to  the  hydrochloric  acid  alone,  and  is,  in 
fact,  formed  more  or  less  readily  by  the  action  of  any  acid  on 
potassium  ferricyanide.  Its  preparation  by  former  experi- 
menters can  thus  be  readily  explained,  as  their  operations 
were  all  carried  on  in  acid  solutions. 

In  our  first  experiments  to  investigate  this  point  we  used 
the  same  quantity  of  hydrochloric  acid  as  in  the  preparation 
of  the  salt  with  potassium  chlorate,  that  is,  the  amount  re- 
quired according  to  the  equation  given  by  Skraup, 

6K8Fe(CN)6  +  KC108  +  6HC1  =  6K2Fe(CN)6  +  7KC1  +  3H20, 

and  otherwise  performed  the  experiments  exactly  as  described 
in  our  previous  article.  50  g.  of  potassium  ferricyanide 
were  dissolved  in  100  c.  c.  of  water,  heated  to  boiling,  and  18 
c.  c.  of  concentrated  hydrochloric  acid  (sp.  gr.  1.19),  diluted 

*  Amer.  Chem.  Jour.,  xxi,  May,  1895. 

t  Ibid.,  193.  }  Ann.  Chem.  (Liebig),  clxxxix,  368. 


FIG.  I. — Potassium  /3-ferricyanide. 


FIG-  II. — Potassium  a-ferricyanide. 


FORMATION  OF  POTASSIUM  p-FERRICYANIDE.       131 

with  three  times  their  volume  of  water,  were  added,  and  the 
mixture  allowed  to  stand  on  the  water-bath.  Small  portions 
were  taken  out  at  short  intervals,  cooled,  precipitated  with 
equal  volumes  of  95  per  cent  alcohol,  and  the  precipitates 
filtered  off.  These  various  preparations  were  then  tested  with 
bismuth  nitrate,  with  which  the  a-ferricyanide  gives  a  yellow 
precipitate,  and  the  /3-ferricyanide  none.  Subsequently  the 
percentages  of  cyanogen  which  they  contained  were  determined 
by  reduction  with  sodium  amalgam,  and  titration  to  potassium 
a-ferricyanide  with  potassium  permanganate.* 

Two  samples  of  the  solution,  taken  out  after  the  reaction 
had  proceeded  one  and  one-half  minutes  and  three  minutes, 
respectively,  gave  with  alcohol  yellow  and  yellowish-green 
precipitates,  the  colors  of  which  were  due  to  the  presence  of 
unchanged  a-ferricyanide.  These  showed,  with  bismuth 
nitrate,  the  test  characteristic  of  the  latter.  At  the  end  of  five 
minutes  the  originally  reddish-yellow  solution  had  assumed  the 
peculiar  red-violet  color  of  the  /3-salt,  and  the  precipitated 
samples  then  consisted  of  a  completely  homogeneous  mass  of 
well-formed,  olive-green  crystals.  These  showed  all  the 
properties  of  potassium  /3-ferricyanide,  K8Fe(CN)6.H2O,  as 
previously  described  by  us.  They  are  most  readily  recognized 
by  their  very  characteristic  crystal-habit,  showing  the  forms 
illustrated  in  Fig.  1.  This  is  taken  from  a  photomicrograph,  as 
is  also  Fig.  2,  which  shows  crystals  of  the  normal  ferricyanide 
obtained  under  similar  conditions.  At  the  same  time  the  per- 
centage of  cyanogen  rapidly  fell  to  a  value  corresponding 
closely  to  that  calculated  for  the  yS-salt;  that  is,  44.96  per 
cent.  The  sample  obtained  after  the  reaction  had  proceeded 
for  ten  minutes  was  of  a  greenish-black  color,  and  showed  no 
distinct  crystallization,  indicating  that  further  decomposition 
had  taken  place.  In  this,  and  subsequent  samples  also,  the 
percentage  of  cyanogen  had  fallen  considerably  below  the 
value  for  the  /3-compound. 

The  analytical  results  of  this  series  of  experiments  are 
tabulated  below : 

*  Amer.  Chem.  Jour.,  xxi,  193. 


132 


ON  THE  FORMATION  OF 


Series  A. 

50  g.  K8Fe(CN)6 ;  18  c.  c.  cone.  HC1. 

1  c.  c.  KMn04  solution  =  0.03704  g.  K8Fe(CN)6. 


No. 

Time. 

Color. 

M 

d  3 

C)  | 

0  B 

0.2 

Min. 

* 

I 

n 

yellow 

0.1881 

4.9 

4.81 

5.08 

45.74 

II 

3 

yellowish-green 

0.2616 

6.8 

6.70 

7.06 

45.65 

III 

5 

olive 

0.2073 

5.3 

5.31 

5.59 

44.89 

IV 

7£ 

olive 

0.2919 

7.4 

7.47 

7.88 

44.52 

V 

10 

green-black 

0.2376 

5.9 

6.08 

6.42 

43.60 

VI 

15 

green-black 

VII 

20 

green-black 

0.3014 

7.3 

7.71 

8.17 

42.53 

Cyanogen  calculated  for  K3Fe(CN)6,  47.41  per  cent. 

"  «          "  K8Fe(C:N")6.H20,  44.96  per  cent. 


The  question  next  suggested  itself,  whether  it  was  neces- 
sary to  have  hydrochloric  acid  present  in  definite  molecular 
quantity,  as  above,  or  whether  its  action  was  not  merely  one 
of  catalysis,  and  caused  by  the  presence  even  of  small  quanti- 
ties. In  order  to  decide  this,  experiments  similar  to  the  above 
were  made,  hi  which  one-half,  one-fourth,  and  one-eighth  of  the 
amount  of  the  acid  there  used  was  employed.  It  was  found, 
not  only  that  the  /3-compound  was  formed  in  each  case,  but 
that  its  subsequent  decomposition  by  the  acid  takes  place 
much  more  slowly  than  when  the  acid  is  more  concentrated. 
The  reactions  could,  therefore,  be  much  more  easily  followed 
in  these  experiments,  as  a  considerable  interval  elapsed  between 
the  point  at  which  the  a-salt  disappeared  and  that  at  which 
the  /3-salt  noticeably  began  to  decompose.  The  results  of 
these  experiments  are  tabulated  below: 


POTASSIUM  p-FERRICYANIDE. 


133 


Series  B. 
50  g.  K8Fe(CN)8 ;  9  c.  c.  cone.  HCi. 


it 

•83 


No.    Time.  Color.  |£to 

Min.  g. 

I       5  yellowish-green  0.2152 

II     10  olive  0.2222 

III  15  olive  0.2233 

IV  20  green-black  0.2155 
V    25  green-black  0.2393 

Series  C. 


50  g.  K8Fe(CN)8 ;  4.5  c.  c.  cone.  HCI. 


fife 


i&A 


II 


5.6 

5.51 

5.81 

45.74 

5.7 

5.68 

5.90 

45.03 

5.7 

5.72 

6.03 

44.82 

5.2 

5.52 

5.82 

42.37 

5.7 

6.12 

6.49 

41.83 

I 

2 

yellow 

0.3535 

9.3 

9.05 

9.54 

46.19 

II 

4 

yellowish-green 

0.3421 

8.9 

8.75 

9.24 

45.68 

III 

6 

olive 

0.1901 

4.9 

4.86 

5.13 

45.26 

IV 

8 

olive 

0.2569 

6.6 

6.57 

6.94 

45.11 

V 

10 

olive 

0.2263 

5.8 

5.79 

6.11 

45.00 

VI 

15 

olive 

0.2223 

5.7 

5.69 

5.90 

45.03 

VII 

20 

green 

0.1994 

5.0 

5.10 

5.38 

44.03 

VIII 

25 

green-black 

0.3195 

8.0 

8.18 

8.63 

44.00 

IX 

30 

green-black 

0.2198 

5.5 

5.63 

5.93 

43.94 

In  Series  D  it  will  be  seen  that  in  the  first  fifteen  minutes 
the  percentage  of  cyanogen  fell  from  the  value  calculated  for 
the  a-salt,  or  47.41  per  cent,  to  45.02  per  cent,  or  nearly  the 
value  calculated  for  the  yS-salt,  a  loss  of  2.4  per  cent.  From 
this  point  on,  the  precipitated  samples  gave  no  reactions  with 
bismuth  nitrate.  During  the  next  twenty  minutes  the  per- 
centage of  cyanogen  fell  only  0.45  per  cent,  and  the  fractions 
taken  out  in  this  interval  were  all  thoroughly  homogeneous 
and  well  crystallized.  Beyond  this  point  the  decomposition 
again  became  more  rapid,  and  the  samples  obtained  were  of 
far  less  satisfactory  appearance  than  those  in  numbers  III-VI. 


134 


ON  THE  FORMATION  OF 


Series  D. 
50  g.  K,Fe(CN), ;  2.25  c.  c.  cone.  HC1. 

la  ^ 


S&A 

111 


No. 

II 
III 

IV 

V 

VI 

VII 

VIII 

IX 

X 

XI 
XII 


Time. 
Min. 

5 

10 
15 
20 
25 
35 
45 
55 
65 

Hours. 

1* 

0 


Color. 

yellow 

yellow 

yellowish-green 

olive 

olive 

olive 

olive 

green 

green-black 

green-black 
green-black 
green-black 


!j 

H 

ti 

««» 

M|I 

I! 

0.2256 

5.9 

5.77 

6.06 

45.92 

0.1510 

3.9 

3.86 

4.08 

45.02 

0.2121 

5.4 

5.43 

5.73 

44.71 

0.2584 

6.6 

6.61 

6.98 

44.85 

0.2639 

6.7 

6.75 

7.12 

44.57 

0.2113 

5.3 

5.41 

5.70 

44.04 

0.2036 

5.0 

5.21 

5.50 

43.12 

0.2171 

5.4 

5.55 

5.86 

43.67 

0.1745 

4.2 

4.46 

4.71 

42.27 

0.2015 

4.9 

5.17 

5.42 

42.70 

0.2010 

4.5 

5.14 

5.43 

39.31 

In  Series  B  and  0  similar  results  were  obtained,  but  the  re- 
actions proceeded  much  more  rapidly.  In  (7,  for  instance,  the 
samples  ceased  to  react  with  bismuth  nitrate  in  eight  minutes, 
and  the  #-salt  was  noticeably  decomposed  at  the  end  of 
twenty  minutes.  It  must,  therefore,  be  concluded  that  the 
velocity  of  the  reaction  is  directly  dependent  upon  the  concen- 
tration of  the  acid. 

Similar  results  were  obtained  when  other  acids  were  substi- 
tuted for  hydrochloric  acid.  Experiments  were  instituted 
with  sulphuric,  oxalic,  and  acetic  acids.  No  quantitative  de- 
terminations were  made,  however,  as  it  was  found  impossible, 
in  the  first  two  cases,  to  obtain  the  precipitates  free  from 
potassium  sulphate  and  potassium  oxalate.  But  that  the  re- 
action proceeded  in  the  same  way  as  when  hydrochloric  acid 
was  used,  was  readily  recognized  by  the  color  of  the  solution 
and  by  the  appearance  of  the  precipitates.  With  oxalic  acid 
the  /3-salt  was  formed  less  readily  than  with  sulphuric  acid, 


POTASSIUM  fr-FERRICYANIDE.  135 

though  in  both  cases  the  conversion  of  the  a-salt  into  its  iso- 
mer  took  place  more  slowly  than  it  did  in  hydrochloric  acid 
solution.  It  would  thus  appear  that  the  catalytic  action  of 
different  acids,  to  which  the  formation  of  the  /3-salt  is  due,  is 
directly  dependent  upon  the  degree  to  which  the  acid  used 
undergoes  ionization.  According  to  this,  an  acid  such  as 
acetic,  which  ionizes  but  slightly,  should  have  only  a  very 
slow  action.  This  was  found  to  be  the  case,  for  with  dilute 
acetic  acid  we  could  obtain  no  /3-salt  at  all,  and  a  solution  of 
ferricyanide,  heated  for  an  hour  with  the  concentrated  acid 
(2  molecules),  still  gave  a  slight  precipitate  with  bismuth 
nitrate. 

NEW  HAVEN,  February,  1899. 


ON  THE  SEPARATION   OF  TUNGSTIC  AND 
SILICIC   ACIDS. 

BY  H.  L.  WELLS  AND  F.  J.  METZGER. 

IN  a  recent  number  of  a  German  periodical*  appears  an 
article  by  Otto  Herting  of  Philadelphia  in  which  the  assertion 
is  made  that  the  method  given  in  the  text-books  for  expelling 
silica  from  tungstic  acid  by  means  of  hydrofluoric  acid  is  incor- 
rect. This  statement  is  made  on  the  ground  of  alleged  numer- 
ous quantitative  experiments  with  mixtures  of  pure  tungstic 
acid  and  pure  ignited  silicic  acid,  but  no  details  in  regard  to 
the  results  are  given.  Herting  believes  that  upon  ignition 
silicic  and  tungstic  acids  form  a  silico-tungstic  acid  which  is 
volatile  when  treated  with  hydrofluoric  acid,  and  finally  says 
that  he  should  be  pleased  if  by  means  of  his  article  he  should 
bring  about  the  more  careful  study  of  the  "  action  of  hydro- 
fluoric acid  upon  tungstic  acid  in  the  presence  of  silicic  acid." 

Since  Herting's  statement  throws  doubt  upon  a  method  that 
is  generally  used,  we  have  undertaken  an  examination  of  the 
matter.  For  this  purpose  we  dissolved  some  of  Kahlbaum's 
tungstic  acid  in  ammonia,  precipitated  with  nitric  acid,  washed 
with  water  by  decantation,  digested  repeatedly  with  sulphuric 
acid  of  sp.  gr.  1.378  to  separate  any  molybdic  acid  that  might 
possibly  be  present,!  washed  the  residue  and  ignited  it.  The 
tungstic  acid  thus  prepared  was  used  for  the  experiments  that 
follow. 

A  weighed  quantity  of  tungstic  acid  in  a  platinum  crucible 
was  mixed  with  about  an  equal  quantity  of  pure  silica.  The 
mixture  was  covered  with  dilute  sulphuric  acid,  a  liberal 
amount  of  pure  hydrofluoric  acid  was  added,  the  liquid  was 
carefully  evaporated  and  the  residue  was  ignited  over  a  Bun- 

*  Zeitschr.  f.  angew.  Chem.,  1901,  165. 

t  See  Ruegenberger  and  Smith,  Jour.  Amer.  Chem.  Soc.,  xxii,  772. 


SEPARATION  OF  TUNGSTIC  AND  SILICIC  ACIDS.       137 

sen  burner.  Then  another  portion  of  silica  was  added  and  the 
operation  was  repeated.  The  results  are  shown  in  the  follow- 
ing table : 

Taken.  WO3  found  after 

WO,  SiO,  1st  operation.        2d  operation. 

I 1928  .2  .1927  .1928 

II 2097  .2  .2097  .2096 

III 2100  .2  .2099  .2100 

IV 1999  .2  .2000  .1998 

The  greatest  error  found  in  these  experiments  is  .0001  g., 
and  they  show  that  the  process  is  perfectly  exact  under  these 
conditions. 

Other  experiments  showed  that  long  ignition  of  the  mixed 
tungstic  and  silicic  acids  over  the  Bunsen  burner  before  expel- 
ling the  silicic  acid  had  absolutely  no  effect  upon  the  results. 

It  was  thought  that  in  the  absence  of  sulphuric  acid  a  loss 
might  occur  by  the  treatment  of  tungstic  acid  with  hydro- 
fluoric acid,  and  the  following  experiments  were  made  to  test 
this  point,  no  sulphuric  acid  being  used :  — 

Taken.  Found. 

WO,  SiO,  WO8 

g-  g-  g- 

.1983  .2  .1983 

.2102  .2  .2100 

.2106  .2  .2105 

.1996  .2  .1994 

In  these  experiments  the  greatest  error,  .0002  g.,  is  well 
within  reasonable  limits ;  hence  it  is  evident  that  the  absence 
of  sulphuric  acid  has  no  effect.  It  is  to  be  noticed  that  in 
these  cases  also  the  tungstic  acid  was  ignited  by  the  Bunsen 
flame  only. 

Attention  should  be  called  to  the  fact  that  tungstic  acid 
must  not  be  ignited  by  means  of  the  blast-lamp,  since  at  the 
temperature  thus  produced  it  volatilizes  to  a  considerable  ex- 
tent. The  books  of  reference  do  not  give  proper  warning  in 
regard  to  this  matter.  The  following  table  gives  the  results 
of  a  series  of  experiments  made  by  heating  over  the  blast-lamp 


138       SEPARATION  OF  TUNGSTIC  AND  SILICIC  ACIDS. 

in  a  platinum  crucible  some  of  the  substance,  which  showed  no 
loss  of  weight  over  the  Bunsen  burner. 

Weight  of  WO8.  Loss. 

Taken 3007 

Ignited  for  2  minutes 2978  .0029 

«         "         "        again    .     .     .     .2962  .0016 

«         "         «  "...    .2946  .0016 

«         "         "  "...     .2932  .0014 

«         "         «  "...     .2924  .0008 

"         "         «  "...     .2916  .0008 

«         "         "  "...     .2906  .0010 

"         5         "  "...    .2872  .0034 

Total  loss,  .0135 

All  the  ignitions  except  the  last  were  made  with  a  lamp  pro- 
vided with  a  water-blast,  which  gave  a  flame  of  only  moderate 
power.  The  last  ignition  was  made  with  a  lamp  connected 
with  a  foot-bellows,  which  gave  a  considerably  higher  tempera- 
ture. It  is  noticeable  that  the  losses  show  a  tendency  to  di- 
minish after  the  first  ignition,  but  this  is  probably  due  to  a 
change  in  the  physical  condition  of  the  oxide  rather  than  to 
the  removal  of  some  more  volatile  substance.  It  is  hardly 
possible  that  our  carefully  purified  tungstic  acid,  which  showed 
no  loss  when  heated  with  a  good  Bunsen  burner,  could  contain 
an  amount  of  molybdic  acid  or  other  volatile  substance  suffi- 
cient to  give  the  results  that  have  been  obtained.  The  loss 
shown  in  the  table  above  amounts  to  nearly  5  per  cent,  while 
in  another  experiment  .1955  g.  of  tungstic  acid  lost  over  7  per 
cent  after  heating  with  the  blast-lamp  for  twenty  minutes.  It 
should  be  stated  that  the  platinum  crucible  in  which  these 
ignitions  were  made  showed  no  loss  in  weight  after  it  had 
been  cleaned. 

We  have  shown  that  Herting's  criticism  of  the  usual  method 
for  separating  silicic  and  tungstic  acids  is  without  foundation, 
and  it  appears  probable  that  his  difficulties  were  due  to  ignite 
ing  tungstic  acid  at  a  too  elevated  temperature. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
April,  1901. 


ON  A  SALT   OF  QUADRIVALENT  ANTIMONY. 

BY  H.  L.  WELLS  AND  F.  J.  METZGER. 

WHILE  engaged  in  purifying  some  caesium  material,  we 
precipitated  a  large  quantity  of  the  salt  Cs3Sb2Cl9  by  adding 
an  excess  of  antimony  trichloride  to  a  hydrochloric  acid  solu- 
tion of  impure  caesium  chloride.  A  small  amount  of  caesium 
remained  in  the  filtrate,  and,  wishing  to  recover  this,  we  added 
some  lead  nitrate  solution,  and  passed  chlorine  gas  into  the 
liquid  in  order  to  precipitate  the  very  insoluble  lead  tetra- 
chloride  salt,  Cs2PbCl6.*  Much  to  our  surprise,  the  pre- 
cipitate, while  showing  the  usual  octohedral  form,  was  bright 
green  hi  color,  whereas  the  pure  lead  salt  is  bright  yellow. 
The  product  was  found  to  contain  a  small  quantity  of  anti- 
mony, and  by  preparing  the  lead  salt  after  the  addition  of 
varying  quantities  of  antimony  trichloride  we  obtained  prod- 
ucts of  various  colors,  from  yellowish  green  to  dark  bluish 
green.  The  following  determinations  were  made  in  a  lighter 
and  a  darker  product : 

Light  green.  Dark  green. 

Antimony    .     .     .     0.92  per  cent  1.44  per  cent 

These  results  indicated  that  antimony  was  not  an  essential 
constituent  of  the  compound,  and  it  seemed  probable  that 
some  salt  of  antimony  isomorphous  with  Cs2PbCl«  had  crys- 
tallized with  it.  We  drew  the  further  inference  that  the 
isomorphous  antimony  compound  must  be  strongly  colored, 
probably  blue.  Fortunately  we  had  access  to  the  reprint  of 
an  article  by  Setterberg  f  (which,  as  far  as  we  can  find,  has 
not  been  noticed  in  any  of  the  books  of  reference)  where  a 
peculiar  black  caesium-antimony  salt  is  described.  Setterberg 

*  Amer.  Jour.  Sci.  (3),  xlvi,  180. 

t  Ofversigt  K.  Vetensk.-Akad.  Forhandl.,  1882,  23. 


140  ON  A    SALT  OF 

made  this  compound  by  boiling  a  solution  of  antimony  tri- 
chloride in  strong  hydrochloric  acid  with  antimony  penta- 
chloride  and  caesium  chloride  in  excess.  He  ascribes  to  it 
the  formula  2CsCLSbCl4  or  4CsCl.SbCl8.SbCl6,  and  states 
that  it  forms  black,  very  small,  short  prisms.  It  was  evi- 
dent that  a  salt  of  this  composition  might  be  expected  to 
crystallize  with  2CsCl.PbCl4,  and  if  so,  the  fact  would  be  a 
strong  argument  in  favor  of  Setterberg's  first  formula,  but 
his  description  of  the  form  of  the  salt  gave  no  evidence  of 
the  isomorphism  of  the  two  compounds. 

We  have  prepared  Setterberg's  salt  under  varying  con- 
ditions, and  have  confirmed  his  formula,  as  is  shown  by  the 
following  analysis  of  a  very  pure  product  : 


Pound. 

Caesium       .....    44.92  44.41 

Antimony   .....    20.23  20.03 

Chlorine     .....     35.13  35.56 

100.28  100.00 

As  far  as  can  be  judged  by  careful  microscopic  examination, 
this  salt  crystallizes  in  perfect  octahedra.  We  could  find  no 
indication  of  a  prismatic  form  corresponding  to  Setterberg's 
description  ;  hence  it  is  probable  that  his  crystals  were  so  small 
that  he  did  not  make  them  out  clearly.  No  optical  exami- 
nation of  the  crystals  could  be  made  on  account  of  their 
complete  opacity.  The  color  of  the  crystallized  substance  is 
absolutely  black,  but  when  a  little  of  it  is  rubbed  between  the 
ground  surfaces  of  a  glass-stoppered  bottle,  it  shows  a  very 
strong,  dark  blue  color. 

From  the'  crystalline  form  and  color  of  this  curious  salt 
there  can  be  no  doubt  that  it  was  the  substance  which  gave 
the  green  color  to  our  products  of  Cs2PbCl6,  and  it  seems 
certain  that  the  two  salts  are  isomorphous.  The  color  of  the 
antimony  salt  indicates  that  it  is  not  a  compound  containing 
antimony  trichloride  and  pentachloride,  for  the  known  cae- 
sium double  salts  with  these  chlorides,  3CsC1.2SbCl8  and 


QUADRIVALENT  ANTIMONY.  141 

CsCl.SbCls,*  are  colorless  or  nearly  so,  We  are  convinced, 
therefore,  that  this  black  salt,  Cs2SbCl«,  is  a  member  of  the 
well-known  group  of  octahedral  double  halides  of  quadriva- 
lent elements,  among  which  are  K2PtCl6,  Cs2SrCl«,  Cs2TeCl6, 
Cs2TeI6,  K2PbCl6,  and  Cs2PbCl8,  and  that  it  is  a  double  salt 
of  antimony  tetrachloride,  SbCl4. 

Judging  from  the  color  of  the  double  salt,  the  tetrachloride 
SbCl4  must  be  black.  This  color  would  be  entirely  unex- 
pected, since  SbCls  and  SbCl5  are  colorless.  We  have  tried 
in  vain  to  get  some  evidence  of  the  separate  existence  of  a 
black  chloride  by  making  mixtures  of  the  two  known  chlorides 
at  low  and  high  temperatures  and  by  treating  the  salt  CsaSbCle 
with  cold  concentrated  sulphuric  acid. 

The  oxide  of  antimony  Sb2O4,  or  SbO2,  is  usually  regarded 
as  a  compound  of  Sb2O8  and  Sb2O6.  It  is  possible  that  this 
may  be  a  true  dioxide,  but  it  would  be  expected  that  an  oxide 
which  corresponded  to  a  black  chloride  would  be  black  also, 
for,  if  there  is  a  difference  in  color,  oxides  are  usually  darker 
than  the  corresponding  chlorides. 

We  have  prepared  a  jet-black  double  bromide  by  using  a 
method  exactly  similar  to  that  by  means  of  which  the  bkck 
double  chloride  was  made.  Judging  from  analogy,  this  is 
probably  Cs2SbBr6,  but  we  were  unable  to  get  a  product  that 
was  pure  enough  for  analysis,  as  it  was  always  mixed  with 
more  or  less  light^colored  impurity.  We  attempted,  without 
success,  to  make  the  corresponding  iodide  and  fluoride. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
April,  1901. 

*  Setterberg,  loc.  cit. 


ON  THE  PURIFICATION  OF  CJESIUM  MATERIAL. 

BY  H.  L.  WELLS. 

SEVERAL  years  ago  *  I  recommended  the  use  of  the  yellow 
salt  2CsCl.PbCl4  as  a  means  of  precipitating  caesium  from  its 
solutions.  Subsequent  experience  has  shown  that  the  method 
is  very  convenient  for  removing  small  quantities  of  the  rare 
metal  from  all  sorts  of  solutions,  particularly  from  those  from 
which  the  greater  part  of  it  has  been  precipitated  by  other 
means.  For  large  quantities  of  caesium,  however,  the  lead 
tetrachloride  method,  used  alone,  is  inconvenient  on  account 
of  the  large  amount  of  chlorine  that  must  be  used,  and  because 
it  is  possible  to  obtain  only  very  dilute  solutions  of  lead  chlo- 
ride or  of  the  white  double  salt  CsC1.2PbCl2.t 

I  have  used  extensively  the  salt  just  mentioned,  as  a  means 
of  precipitating  caesium  from  concentrated  solutions  of  the 
crude  extract  of  pollucite  made  by  means  of  hydrochloric  acid. 
The  precipitation  is  made  by  adding  a  hot,  concentrated  solu- 
tion of  the  calculated  amount  of  lead  nitrate.  The  precipitate 
is  crystalline  and  can  be  readily  washed  with  dilute  hydro- 
chloric acid,  then  it  can  be  very  easily  decomposed  by  boiling 
with  ammonium  carbonate  solution.  The  method  is  satisfac- 
tory in  a  case  where  very  little  potassium  and  practically  no 
rubidium  are  present,  for  although  it  does  not  give  a  good 
separation  from  these  metals,  the  precipitation  of  caesium  is 
nearly  complete.  The  precipitate  CsC1.2PbCl2,  however,  is 
very  heavy  compared  with  the  amount  of  caesium  that  it  con- 
tains, and  its  decomposition  with  ammonium  carbonate  pro- 
duces four  molecules  of  ammonium  chloride  for  one  of  caesium 
chloride.  For  these  reasons  the  method  has  been  abandoned 
in  this  laboratory  in  favor  of  the  method  of  Godeffroy. 

*  Amer.  Jour.  Sci.  (3),  xlvi,  186.  f  Ibid.  (3),  xlv,  121. 


PURIFICATION  OF  CAESIUM  MATERIAL.  143 

In  precipitating  caesium  according  to  GodefTroy's  method 
I  am  accustomed  to  use  less  concentrated  hydrochloric  acid 
solutions  than  those  that  have  been  recommended.  About  one- 
third  or  one-half  of  the  total  volume  of  concentrated  hydro- 
chloric acid  answers  very  well,  and  a  solution  of  this  kind 
possesses  the  advantage  that  it  can  be  filtered  by  means  of 
paper.  To  such  a  solution  antimony  trichloride,  also  dissolved 
in  hydrochloric  acid,  is  added  as  long  as  a  precipitate  forms. 
The  latter  is  collected,  best  on  a  Biichner  filter,  and  well  washed 
with  cold  dilute  hydrochloric  acid. 

To  the  filtrate  and  washings  from  the  antimony  salt,  with- 
out concentrating  them,  lead  nitrate  is  added  at  the  rate  of  2 
or  3  g.  per  liter.  This  salt  should  be  dissolved  in  water  before 
it  is  added.  Chlorine  gas  is  then  passed  in  until  the  solution 
is  saturated  with  it.  After  standing  for  a  few  hours  the  liquid 
is  decanted  from  the  precipitate  of  Cs2PbCl6  (which  is  usually 
colored  green  from  the  presence  in  it  of  the  dark  blue  salt 
Cs2SbCl6*)  and  is  tested  by  the  addition  of  a  little  more  lead 
nitrate,  and  chlorine  also  if  necessary.  This  precipitation  is 
so  complete,  as  far  as  caesium  is  concerned,  that  the  liquid  may 
be  finally  discarded.  A  liter  of  such  a  liquid  will  probably 
hold  in  solution  only  about  0.1  g.  of  Cs2PbCl6,  but  the  rubid- 
ium salt  is  nearly  100  times  more  soluble.  The  lead  tetra- 
chloride  salt  should  be  washed  on  a  Biichner  funnel  with  cold, 
dilute  hydrochloric  acid. 

Formerly  I  was  accustomed  to  decompose  the  antimony 
salt  3CsC1.2SbCl8  f  by  suspending  it  in  water  and  pass- 
ing in  hydrogen  sulphide  gas,  but  for  large  quantities  this  is 
a  very  slow  and  laborious  operation,  and  it  is  much  more 
convenient  to  treat  it  in  a  large  porcelain  dish  with  boiling 
dilute  ammonium  hydroxide.  The  antimonious  oxide  thus 
produced  is  dense  and  easy  to  filter  and  wash ;  moreover  it 

*  Concerning  this  compound,  see  the  preceding  article. 

t  The  composition  of  this  compound  was  very  incorrectly  determined  by 
Godeffroy,  who  gave  it  the  formula  6CsCl.SbCl8.  Setterberg  first  arrived 
at  the  correct  formula,  which  was  afterwards  confirmed  by  Remsen  and 
SaunderS;  and  also  by  Muthmann,  and  by  Wells  and  Foote. 


144  ON  THE  PURIFICATION  OF 

may  be  readily  dissolved  in  hydrochloric  acid  and  used  again 
for  precipitating  caesium.  A  little  antimony  goes  into  solu- 
tion in  the  ammonia,  but  this  is  readily  removed,  best  after  the 
liquid  has  become  slightly  acid  by  evaporation,  by  passing  in 
hydrogen  sulphide  and  filtering. 

The  removal  of  ammonium  chloride  on  a  large  scale  by 
ignition  is  a  very  slow  operation.  It  is  therefore  best,  in 
most  cases,  after  the  hydrogen  sulphide  has  been  removed  by 
evaporation,  to  add  to  the  concentrated  solution  of  caesium 
and  ammonium  chlorides,  in  a  large  porcelain  dish,  a  liberal 
amount  of  concentrated  nitric  acid  and  to  heat  cautiously 
until  frothing  has  ceased.  When  further  additions  of  strong 
nitric  acid  produce  no  change  of  color  or  evolution  of  gas 
upon  heating,  the  ammonium  salts  are  entirely  destroyed  and 
the  caesium  chloride  changed  to  nitrate.*  The  solution  of 
caesium  nitrate  in  nitric  acid  is  then  evaporated  to  dryness, 
and  the  residue  is  heated  until  the  acid  nitrate  f  is  decom- 
posed, and  the  normal  nitrate  is  more  or  less  completely 
fused.  The  evaporation  to  dryness  of  the  nitrate  in  the 
presence  of  nitric  acid  over  a  free  flame  in  a  dish  is  not  a 
difficult  operation,  since  decrepitation  takes  place  to  a  much 
less  extent  than  is  the  case  when  the  chloride  is  evaporated 
in  the  same  way.  A  large  mass  of  fused  caesium  nitrate 
should  not  be  allowed  to  solidify  quietly  in  the  bottom  of  a 
porcelain  dish,  for  on  cooling  it  is  liable  to  break  the  dish  by 
its  contraction.  If  it  is  stirred  as  it  solidifies,  this  danger  is 
avoided. 

Caesium  nitrate  is  one  of  the  most  beautiful  of  salts  for 
recrystallization.  Like  potassium  nitrate,  it  is  much  more 
soluble  in  hot  water  than  in  cold,  and  it  crystallizes  upon 
slowly  cooling  a  hot  concentrated  solution  in  the  form  of  large 
colorless  prisms.  I  have  found  that  recrystallizing  this  salt 
tends  to  purify  it  from  traces  of  rubidium,  for  a  large  quantity 

*  This  method  of  destroying  ammonium  chloride  is  due  to  J.  Lawrence 
Smith.  See  Amer.  Jour.  Sci.  (2),  xxxiv,  367. 

t  A  description  of  the  acid  caesium  nitrates  will  be  published  soon  from 
this  laboratory. 


CAESIUM  MATERIAL.  145 

of  the  salt  which  showed  no  rubidium  spectrum,  upon  sys- 
tematic recrystallization  showed  a  distinct  spectrum  for  that 
metal  in  the  final  mother-liquor.  This,  however,  is  a  slow 
method  of  purification  if  it  is  desired  to  carry  the  latter  to  the 
last  degree,  but  the  nitrate  obtained  by  one  or  two  recrystalli- 
zations  is  pure  enough  for  any  ordinary  purpose,  unless  the 
original  antimony  salt  was  contaminated  to  an  unusual  extent. 

The  nitrate  is  readily  converted  into  carbonate  by  mixing  it 
with  two  parts  of  pure  oxalic  acid,  adding  a  little  water, 
evaporating  to  dryness  and  fusing  the  residue  in  a  platinum 
crucible.* 

Where  the  highest  degree  of  purity  in  a  caesium  salt  is 
desired,  the  salt  CsCl2I  t  by  its  recrystallization  probably 
offers  one  of  the  best  means  for  accomplishing  that  object. 
It  is  enormously  less  soluble  than  the  corresponding  rubidium, 
potassium,  sodium,  and  lithium  salts.  I  have  found  that  this 
salt  may  be  made  very  conveniently  from  the  nitrate  by  dis- 
solving one  part  of  the  latter  together  with  one  atomic  pro- 
portion of  iodine  in  about  ten  parts  of  1  :  1  hydrochloric  acid 
at  a  temperature  just  below  boiling.  The  solution  takes 
place  quickly,  and,  upon  cooling,  the  beautiful  yellow  salt 
crystallizes  out.  It  is  recrystallized  by  solution  in  hot  1  :  1 
hydrochloric  acid  and  cooling.  One  or  two  recrystallizations, 
when  each  crop  is  well  drained  and  washed  with  a  little  cold 
dilute  hydrochloric  acid,  give,  even  from  impure  materials,  a 
remarkably  pure  product.  From  this  trihalide  by  ignition, 
best  at  a  very  gentle  heat  so  that  the  mass  does  not  fuse, 
pure  caesium  chloride  may  be  prepared. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
April,  1901. 

*  Method  of  J.  Lawrence  Smith,  loc.  cit. 
t  Amer.  Jour.  Sci.  (3),  xliii,  17. 


10 


ON  THE  ACID  NITRATES. 

BY  H.  L.  WELLS  AND  F.  J.  METZGER. 

A  NUMBER  of  years  ago,  it  was  noticed  by  one  of  us  that  when 
caesium  nitrate  is  evaporated  with  strong  nitric  acid,  the  last 
part  of  the  acid  is  expelled  with  some  difficulty,  and  the 
probable  existence  of  a  rather  stable  acid  nitrate  suggested 
itself.  Mr.  A.  P.  Beardsley,  of  this  laboratory,  undertook  an 
examination  of  the  matter  last  year,  and,  upon  dissolving 
caesium  nitrate  in  hot  nitric  acid  of  sp.  gr.  1.42  and  cooling, 
obtained  beautifully  crystallized  crops  of  the  salt  HNO8. 
CsNO3.  The  circumstances  were  such  that  Mr.  Beardsley's 
work  in  this  direction  was  interrupted,  and  we  have  under- 
taken a  further  examination  of  the  subject.  Ditte*  has  de- 
scribed the  following  list  of  acid  nitrates : 

KN08.2HN08 

NH4N03.HN08 

NH4N03.2HN08 

[2RbN03.5HN08] 

[T1N08.3HN08] 

The  two  formulae  enclosed  in  brackets  do  not  correspond 
to  the  others  nor  to  the  caesium  salt  mentioned  above,  and  we 
have  found  that  they  are  incorrect.  In  making  these  alleged 
compounds,  2RbNO8.5HNO8  and  T1NO8.3HNO8,  Ditte  satu- 
rated "  monohydrated "  nitric  acid  (the  liquid  corresponding 
to  the  formula  HNO8)  with  the  normal  nitrates  and  then 
simply  analyzed  the  solution.  He  had  prepared  the  other  acid 
nitrates  in  the  same  way,  but  in  these  cases,  having  performed 
the  operation  above  their  melting-points,  he  was  able  to  make 
definite  compounds,  and  showed  that  the  solutions  became 
perfectly  solid  at  definite  temperatures. 

*  Ann.  de  Chim.  (5),  xviii,  320  (1878). 


ON  THE  ACID  NITRATES.  147 

We  have  easily  succeeded  in  crystallizing  two  caesium  and 
two  rubidium  acid  nitrates,  and  a  single  thallium  salt,  and  find 
that  the  salts  of  the  last  two  metals  do  not  correspond  to  the 
formulae  given  by  Ditte.  We  have  confirmed  the  composition 
of  his  potassium  acid  nitrate,  and  since  his  ammonium  salts 
correspond  exactly  to  the  caesium  and  rubidium  compounds, 
we  assume  that  they  are  correct.  Our  revision  and  additions 
lead  to  the  following  list  of  acid  nitrates  : 


KN08.2HN08 


KbN08.HN08  KbN08.2HN08 

CsN08.HN08  CsISr08.2HNOg 

.....  T1N08.2HNO, 

These  salts  belong  to  two  types,  of  which  the  diacid  form  is 
evidently  most  readily  produced,  since  thallium  and  potassium 
apparently  do  not  yield  the  other.  The  caesium  salts  are 
more  easily  prepared  and  are  more  stable  than  the  others. 

It  has  been  supposed  that  "  monobasic  "  acids  are  incapable 
of  forming  acid  salts,  and  it  is  evident  that  this  belief  prevails 
at  the  present  tune,  for  the  following  statement  is  made  in  a 
recently  published  text-book  :  "  Acids  like  hydrochloric  and 
nitric  acids  have  not  the  power  to  form  acid  salts.  They 
are  called  monobasic  acids."  This  statement  seems  to  be 
too  sweeping,  for  there  are  many  acid  chlorides,  some 
of  which  are  well  known  and  remarkably  stable;  in  fact, 
their  stability  when  in  solution  apparently  leads  to  the 
opinion  that  they  are  not  real  acid  salts.  The  following  list 
will  serve  as  examples  of  these  compounds:  2HCl.PtCl4  ; 
HCl.AnCl8  ;  2HCl.SnCl4  ;  HCl.ZnCl2.2H  O  ;  2HCl.CuCl  ; 
2HCl.CuCla;  5HCl.SbCl5.10H2O.  Iodides  and  bromides  are 
also  known,  for  example,  2HBr.SnBr4  and  HI.Agl.  The  ease 
with  which  hydrofluoric  acid  forms  acid  salts  is  remarkable,  and 
many  acid  salts  of  univalent  organic  acids,  such  as  acetic, 
propionic,  and  valerianic  acids  are  well-known.  Since  it  is  now 
shown  that  the  acid  nitrates  are  well  defined  and  in  some  cases 
comparatively  stable  bodies,  the  old  idea  that  only  "  polybasic  " 


148  ON  THE  ACID  NITRATES. 

acids  are  capable  of  forming  acid  salts  should  be  entirely 
abandoned.  The  circumstance  that  acid  nitrates  are  not  more 
numerous  is  doubtless  connected  with  the  fact  that  double 
nitrates  in  general  are  rare. 

Method  of  Preparation.  —  The  monoacid  salts  RbNO3.HNO3 
and  CsNO8.HNO8  are  readily  prepared  by  saturating  nitric 
acid  of  sp.  gr.  1.42  with  the  normal  nitrates  at  a  gentle  heat 
and  cooling  to  crystallization.  The  use  of  a  freezing  mixture, 
such  as  ice  and  salt,  is  desirable  in  making  the  rubidium  com- 
pound, but  it  is  not  necessary  for  the  caesium  salt.  Only 
normal  potassium  nitrate  and  thallous  nitrate  could  be  crystal- 
lized from  nitric  acid  of  this  strength. 

The  diacid  salts  KNO3.2HNO3,  RbN08.2HNO3,  CsNO3. 
2HNO8,  and  T1NO3.2HNO8  were  all  prepared  by  dis- 
solving the  normal  nitrates  to  saturation  in  nitric  acid  of 
sp.  gr.  1.50  and  cooling  with  a  freezing  mixture,  usually  con- 
siderably below  0°.  In  preparing  the  thallous  compound 
warming  must  be  avoided,  because  it  causes  the  oxidation  of  a 
part  of  the  thallium  to  thallic  nitrate.  When  this  has  hap- 
pened, we  find  that  the  addition  of  alcohol,  after  the  removal 
of  most  of  the  strong  nitric  acid  by  evaporation,  is  a  convenient 
means  of  converting  thallic  nitrate  into  the  thallous  salt. 

Properties.  —  The  monoacid  salts  RbNO8.HNO8  and 
CsNO3.HNO3  form  large,  flat  masses  of  small,  colorless,  trans- 
parent crystals,  apparently  octahedra,  arranged  in  parallel  po- 
sition. The  diacid  salts  RbNO8.2HNO8  and  T1NO3.2HNO8 
form  beautiful,  colorless,  transparent  needles,  while  CsNO8. 
2HNO8  forms  large,  thin,  colorless,  transparent  plates. 

All  the  acid  nitrates  give  off  nitric  acid  more  or  less  rapidly 
upon  exposure  to  the  air  at  ordinary  temperature.  The  salt 
T1NO8.2HNO8  must  be  dried  on  paper  in  a  very  cool  place, 
as  its  melting-point  is  below  the  ordinary  temperature. 
RbNO3.2HNO8  decomposes  rapidly,  and  this  also  must  be 
prepared  for  analysis  in  a  cool  place.  The  salt  RbNO8.HNO8, 
and  the  two  caesium  salts,  are  more  stable  than  the  others; 
the  monoacid  salts  are  almost  stable  in  the  air,  and  may  be 
preserved  indefinitely  in  hermetically  sealed  tubes. 


ON  THE  ACID  NITRATES.  149 

The  melting-points  of  the  acid  nitrates,  as  given  by  Ditte 
and  found  by  ourselves,  are  as  follows  : 

NH4N08.HN08  ......     9°  (Ditte) 

KbN08.HN08     ......     62° 

CsN08.HN08      ......    100° 

KNOS.2HN08    ......  -3°  (Ditte) 

T1N08.2HN08    ......  Undetermined 

NH4N08.2HN08     .....  18°  (Ditte) 

KbN03.2HN03   ......  39-46° 

CsN03.2HN08    ......  32-36° 

The  melting-points  of  the  rubidium  and  caesium  monoacid 
nitrates  are  sharp,  but  the  corresponding  diacid  salts  melt 
gradually,  evidently  on  account  of  decomposition.  The  salt 
T1NO3.2HNO8  melts  below  the  ordinary  temperature,  but  its 
exact  melting-point  was  not  determined. 

Analyses.  —  The  acid  nitrates  are  very  easily  analyzed. 
The  amount  of  normal  nitrate  was  determined  by  simple  heat>- 
ing,  and  the  amount  of  nitric  acid  by  titration.  The  follow- 
ing analyses  were  made  with  separate  crops  of  the  different 
compounds  : 

Monoacid  Rubidium  Nitrate,  HNO&.RbNO*. 

Calculated.  Found. 

i.  ii.          m. 

HKOS      .    .    .    30.00  30.51     ..."   30.18 

.    .     .     70.00  .  .  .     70.43     .  .  . 

Monoacid  Caesium  Nitrate,  ffNOs-  CsNO*. 

Calculated. 


HN08      .     .     .    24.42  24.23    24.13     .  .  .      24.28 

CsN08     .    .    .     75.58  ......      76.48     75.52 

Diacid  Rubidium  Nitrate,  0HNOs.RbNOs. 


Calculated.  Found. 

i.  n.         m. 


HKOS      .    .    .    46.15  45.79     ...... 

KbN08    .    .     .    53.85  .  .  .     53.74    53.44 

*  Determinations  by  H.  P.  Beardsley. 


150  ON  THE  ACID  NITRATES. 


Diacid  Ccesium  Nitrate, 


Calculated.  Found. 

i.          ii.          ra. 


HN08   ....    39.25            39.23    39.86     .  .  . 
CsN08  ....    60.75  61.22 

Diacid  Thallous  Nitrate,  TlNOs.2HNOz. 


Calculated.  Found. 

i.  H.          m. 


HN08 32.14  33.13    33.02     .  .  . 

T1N08      ....    67.86  67.00 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
April,  1901. 


INVESTIGATIONS   ON  DOUBLE  NITRATES. 
I.  CAESIUM  DOUBLE  NITKATES. 

BY  H.  L.  WELLS  AND  A.  P.  BEARDSLEY. 

COMPARATIVELY  few  double  nitrates  have  been  described, 
and  it  is  a  curious  circumstance  that  most  of  these  are  com- 
pounds of  metals  of  the  rare-earth  group,  as  follows : 

2KN08.Ce(N03)8.2H20 
2NH4N08.Ce(N03)8.4H20 
2NH4N08.La(NO3)8.4H2O 
2NH4N08.Di(N08)3.4H20 

3Mg(N08)2.2Ce(N08)3.24H2O 

3Zn(ko8)2.2Ce(N08)8.24H2O 

3Mn(N03)2.2Ce(N08)3.24H20 

3Co(N03)2.2Ce(N08)8.24H20 

3Ni(N08)2.2Ce  (N08)  8.24H20 

3Mg(N03)2.2La(N08)8.24H20 

3Zn(N08)2.2La(N08)3.24H20 

3Mn(N03)2.2La(N08)8.24H2O 

3Ni(N08)2.2La(N08)8.36H20 

3Zn(N08)2.2Di(N08)8.60H20 

3Ni(N08)2.2Di(N03)8.36H2O 

3Co(N08)2.2Di(N08)8.48H20 

2KN08.Ce(NO,)4.l^H20 
2NH4N08.Ce  (N08)4.l£H20 

In  addition  to  the  above,  the  only  normal  double  nitrates 
that  have  been  found  mentioned  in  the  literature  are  the 
following :  * 

*  There  are  known,  however,  certain  easily  fusible  mixtures  of  nitrates, 
such  as  potassium  and  lead  nitrates,  and  thallous  and  silver  nitrates,  but 
apparently  these  do  not  form  definite,  crystallized  compounds. 


152         INVESTIGATIONS  ON  DOUBLE  NITRATES. 

KN08.Au(N03)3 
2KN08.T1(N08)8.H20 


NH4N08.AgN08 
KN08.AgN08 
3KN08.AgN08(?) 

With  the  exception  of  the  auric  and  thallic  salts,  these  are 
all  compounds  of  an  alkaline  nitrate  with  a  univalent  nitrate. 
It  appears  to  be  a  singular  fact  that  no  double  nitrates  of 
alkaline  and  bivalent  metals  are  known  to  exist. 

Since  caesium  is  known  to  form  double  salts  with  great 
facility,  we  have  attempted  to  prepare  double  nitrates  of  this 
metal  with  several  bivalent  metals  which  generally  form  double 
salts  very  readily.  For  this  purpose  we  selected  lead  nitrate, 
cobalt  nitrate,  and  mercuric  nitrate,  but  after  the  most  careful 
work  we  were  unable  in  either  case  to  obtain  any  definite  crys- 
tallized product,  except  crops  of  the  simple  nitrates  :  In  each 
case  there  was  evidence  of  combination  from  the  fact  that 
solutions  were  obtained  which  were  much  too  concentrated  to 
hold  in  solution  the  caesium  nitrate  that  was  present,  if  it  had 
been  uncombined.  We  conclude,  therefore,  that  double  nitrates 
were  formed  in  solution  in  these  cases,  but  that  they  were  so 
exceedingly  soluble  that  they  could  not  be  crystallized. 

It  seemed  desirable  to  find  if  trivalent  nitrates,  other  than 
those  of  the  rare-earth  metals,  are  capable  of  forming  double 
nitrates  with  caesium  nitrate.  For  this  purpose  we  selected 
ferric  nitrate,  and  succeeded,  although  with  some  difficulty,  in 
preparing  a  double  nitrate. 

Ccesium  Ferric  Nitrate,  CsNOs.Fe(NOB)s.7H20.—This  salt 
is  formed  at  a  rather  low  temperature  in  very  concentrated 
solutions  containing  nitric  acid  and  nearly  equal  molecular 
proportions  of  the  component  salts.  It  forms  pale  yellow, 
deliquescent,  prismatic  crystals,  which  melt,  not  sharply,  at 
33°  -36°.  The  following  analyses  were  made  with  separate 
crops  : 


INVESTIGATIONS   ON  DOUBLE  NITRATES.         153 

Calculated  for  Found. 

CsN03.Fe(N08),.7HtO.         I.               II.  HI. 

Caesium  nitrate  .     .     34.64             .  .  .     35.51  34.87 

Ferric  nitrate      .     .     42.98            42.29    42.73  42.68 

Water 22.38             22.92 

Nitrogen    ....       9.94             9.54 


II.  CESIUM  BISMUTH  NITRATE,  2CsNO3.Bi(NO8)8 . 

By  G.  S.  JAMIESON. 

As  a  continuation  of  the  investigation  just  described,  experi- 
ments have  been  conducted  with  caesium  nitrate  and  bismuth 
nitrate.  The  two  salts  were  dissolved  in  widely  varying  pro- 
portions in  dilute  nitric  acid,  and  the  solutions  were  evapo- 
rated until  crystallization  took  place  on  cooling.  When  2^ 
or  more  molecules  of  caesium  nitrate  to  1  molecule  of  bis- 
muth nitrate  were  present,  the  simple  caesium  salt  crystal- 
lized out;  on  the  other  hand,  when  the  ratio  of  caesium  to 
bismuth  was  less  than  about  l£  to  1,  bismuth  nitrate  was 
obtained.  Between  these  limits  a  double  salt  was  produced, 
particularly  upon  agitating  the  cold  solution,  in  the  form  of 
colorless,  prismatic  crystals  which  are  stable  upon  exposure. 
These  were  sometimes  more  than  a  centimeter  in  length. 
The  salt  melts  at  102°.  Two  crops  gave  the  following 
analyses : 

Calculated  for  Found. 

2CsNO3.Bi(NO8)8.  I.  II. 

Cgesium  nitrate   .     .     .     49.75  47.00    51.22 

Bismuth  nitrate .     .     .     50.25  52.63    48.16 

The  analyses  do  not  agree  very  satisfactorily  with  each  other 
or  with  the  calculated  numbers.  This  was  doubtless  due  to 
the  syrupy  nature  of  the  mother-liquor  which  made  the  drying 
of  the  crystals  by  means  of  filter  paper  a  difficult  matter.  The 
appearance  of  the  crystals,  in  being  homogeneous  and  different 
from  the  separate  nitrates,  however,  leaves  no  doubt  that  this 
is  a  definite  double  nitrate. 


154        INVESTIGATIONS   ON  DOUBLE  NITRATES. 

III.  THAU.OUS  THALLIC  NITRATE,  2TlNO8.Tl(NO8)a. 

By  F.  J.  METZGER. 

When  thallous  nitrate  is  dissolved  in  concentrated  nitric  acid 
(sp.  gr.  1.50)  by  the  aid  of  heat,  a  part  of  the  salt  is  oxidized 
to  thallic  nitrate,  and,  upon  cooling  the  properly  concentrated 
solution,  large,  colorless,  transparent,  prismatic  crystals  are 
formed.  The  salt  is  very  stable  in  dry  air,  but  blackens  when 
exposed  to  moisture.  It  melts  at  150°.  Several  crops,  made 
under  different  conditions,  were  analyzed. 

Calculated  for  Found. 

2T1N03.T1(NO,)S.  I.  II.  IH. 

Thallic  nitrate  .    .    42.30  43.12    43.13     .  .  . 

Total  thallium  .     .    66.37  65.30    65.53    65.30 

The  thallic  nitrate  was  determined  by  titrating  the  iodine 
set  free  by  the  salt  from  potassium  iodide  solution.  The  total 
thallium  was  weighed  as  iodide. 

Conclusions.  —  No  evidence  has  been  obtained  that  alkaline 
nitrates  form  crystallizable  double  nitrates  with  the  nitrates  of 
bivalent  metals. 

Several  trivalent  nitrates,  other  than  those  of  the  rare  earth 
metals,  are  capable  of  forming  double  nitrates. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
April,  1901. 


ON  CAESIUM  PERIODATE  AND 
IODATE-PERIODATE. 

BY  H.L.  WELLS. 

THE  two  salts  to  be  described  were  obtained  as  the  result  of 
an  attempt  to  make  a  thorough  investigation  of  the  caesium 
salts  of  periodic  acid.  In  view  of  the  well-known  complexity 
of  periodates  in  general,  it  was  expected  that  a  considerable 
number  of  caesium  periodates  would  be  found,  and  it  was 
hoped  that  they  might  be  of  much  theoretical  interest.  As 
a  result,  however,  only  normal  caesium  periodate,  CsIO4,  was 
obtained  when  caesium  carbonate  was  added  in  widely  varying 
proportions  to  solutions  of  periodic  acid.  This  was  so  disap- 
pointing that  experiments  upon  the  addition  of  periodic  acid 
to  caesium  hydroxide  solutions,  which  were  originally  planned, 
were  not  carried  out. 

Preparation  of  Periodic  Acid.  —  The  principles  involved  hi 
the  method  used  for  this  purpose  are  not  new,  but  as  some  of 
the  details  may  be  of  use  to  others,  a  brief  description  of  the 
process  is  given.  12.7  g.  of  iodine  are  put  into  a  10  per  cent 
solution  of  60  g.  of  sodium  hydroxide.  The  liquid  is  heated 
to  boiling  in  a  flask,  and  a  rapid  stream  of  chlorine  gas  is 
passed  into  the  continually  boiling  solution  until  the  large 
amount  of  precipitate  suddenly  formed  begins  to  cause  bump- 
ing, when  the  flame  is  instantly  removed,  and  the  stream  of 
chlorine  is  continued  until  no  further  increase  is  observed  in 
the  white  precipitate  of  H3Na2IO<j.  While  the  liquid  is  still 
warm  the  precipitate  is  collected  on  a  Buchner  funnel  and  then 
thoroughly  washed  with  cold  water.  It  is  dried  in  a  steam- 
bath.  The  yield  is  usually  about  22  g.  or  80  per  cent  of  the 
theoretical.  The  sodium  periodate  is  suspended  in  a  large 
volume  of  water,  three  molecules  of  silver  nitrate  in  solution 


156  ON  CAESIUM  PERIOD  ATE 

are  added,  the  liquid  is  boiled,  filtered  hot,  and  the  black  pre- 
cipitate of  Ag8IO6  is  washed  thoroughly  with  water.*  The 
black  silver  periodate  while  still  moist  is  suspended  in  a 
small  amount  of  water,  and  chlorine  gas  f  is  passed  in  persist- 
ently, with  agitation,  until  the  precipitate  has  become  nearly 
white.  The  silver  chloride  is  removed  by  nitration,  the 
liquid  is  concentrated  on  the  water-bath,  then  brought  to 
crystallization  over  sulphuric  acid.  After  being  drained,  the 
beautiful  crystals  of  periodic  acid  are  ready  for  use. 

Ccesium  Periodate,  CsIO^.  —  This  salt  crystallizes  in  white 
plates,  and  is  rather  sparingly  soluble  in  cold  water.  It  was 
formed  upon  adding  small  quantities  of  caesium  carbonate  to 
concentrated  solutions  of  periodic  acid,  and  also  when  larger 
quantities,  up  to  an  excess  of  csesium  carbonate,  were  used. 
It  can  be  recrystallized  readily  by  dissolving  in  hot  water  and 
cooling.  When  a  very  large  excess  of  caesium  carbonate  was 
added  to  a  solution  of  the  salt  and  the  mixture  was  evaporated 
to  the  point  of  crystallization,  more  or  less  caesium  iodate, 
CsIO8,  usually  was  formed  on  account  of  an  accidental  or 
perhaps  spontaneous  reduction,  but  no  evidence  of  the  exist- 
ence of  any  other  periodate  was  thus  obtained.  The  follow- 
ing analyses  of  six  separate  crops  were  made,  most  of  them 
for  the  purpose  of  identification : 


Calculated  fo 

r 

JSOl 

ma. 

Csesium  . 

CsIO4. 

.    41.05 

I. 

42.02 

ii. 
40.37 

III. 

IV. 

V. 

VI. 

Iodine 

.    39.20 

38.19 

Oxygen  . 

.    19.75 

19.62 

19.77 

19.61 

19.45 

19.65 

19.20 

Caesium  was  determined  by  treating  the  substance  with  con- 
centrated sulphuric  acid,  evaporating,  converting  into  normal 

*  The  filtrate  contains  a  considerable  amount  of  periodate  which  is  kept  in 
solution  by  the  nitric  acid  set  free  by  the  reaction.  Most  of  this  may  be 
recovered  in  the  form  of  the  golden  yellow  salt  H3Ag2IO6  by  evaporating  the 
liquid  to  very  small  volume  and  cooling,  or  after  evaporating  to  dryness  on 
the  water-bath  another  crop  of  Ag3IO5  may  be  obtained  by  treatment  with 
water. 

t  According  to  my  experience  chlorine  is  much  better  than  bromine  for 
this  purpose. 


AND  IODATE-PERIODATE.  157 

sulphate  by  ignition  in  air  containing  ammonia,  and  weighing. 
Iodine  was  determined  as  silver  iodide  after  reduction  with 
sulphurous  acid  solution.  Oxygen  was  determined  by  titrat- 
ing with  sodium  thiosulphate  the  iodine  set  free  by  the  sub- 
stance in  a  solution  of  potassium  iodide  in  the  presence  of  an 
acid. 

Acid  Ccesium  lodate-Periodate,  HCsIOzIO^H20. — This 
curious  salt  was  first  noticed  as  having  crystallized  after  spon- 
taneous evaporation  from  a  solution  of  caesium  periodate  in 
dilute  periodic  acid,  in  which  the  periodate  had  suffered  par- 
tial reduction.  A  second  crop  was  purposely  prepared  from 
a  similar  solution,  and  a  third  product  was  made  by  dissolv- 
ing caesium  iodate  and  periodate  in  dilute  periodic  acid  and 
cooling.  It  forms  beautiful,  slender  white  prisms.  The 
three  crops  gave  the  following  results  upon  analysis : 

Calculated  for          Vmu& 

HCBI207.2H20.          "-£—          n  —££ 

Hydrogen    ....  0.19  

Caesium 24.80  .  .  .     24.00     .  .  . 

Iodine 47.39  .  .  .     47.38    47.11 

Oxygen 20.90  20.75    20.58      .  .  . 

Water 6.72  

100.00 

Iodine  as  I205      .     .    23.69  23.20 

Iodine  as  I207      .     .    23.69  23.91 

lodic  acid  was  determined  by  dissolving  the  substance  in 
dilute  nitric  acid,  precipitating  silver  iodate  by  the  addition  of 
silver  nitrate,  and  weighing  the  silver  iodide  resulting  from  its 
ignition.  The  periodic  acid  left  in  the  filtrate  from  the  silver 
iodate  was  reduced  by  the  addition  of  sulphurous  acid,  and  the 
iodine  was  determined  as  silver  iodide. 


ON  THE  PERIODIC  SYSTEM  AND  THE  PROPER- 
TIES OF  INORGANIC  COMPOUNDS.* 

BY  JAMES  LOCKE. 

I.    THE  INSUFFICIENCY  OF  THE  SYSTEM  AS  APPLIED  TO 
COMPOUNDS. 

THE  problems  set  before  the  inorganic  chemist  by  the  periodic 
system,  which  have  directly  or  indirectly  guided  almost  all 
the  inorganic  investigations  of  the  past  thirty  years,  may  be 
divided,  roughly  in  the  abstract  but  very  sharply  in  the  results 
obtained,  into  two  classes.  The  one,  of  the  fruitfulness  of 
which  no  one  can  complain,  deals  with  the  superficial  group- 
relations  which  exist  between  the  members  of  the  various 
families.  Their  solution  leads  to  what  may  be  called  the 
development  of  group  analogies.  The  problems  of  the  second 
class,  on  the  other  hand,  have  either  been  entirely  neglected, 
or  their  study  has  yielded  only  the  most  unsatisfactory  results. 
These  have  had  to  do  with  the  contradictions  of  fact  which 
the  system,  as  formulated  by  Mendel^eff,  involved,  and  to 
which  the  system  should  in  course  of  time  adapt  itself.  But 
all  the  more  important  inconsistencies  which  it  presented  in 
the  year  1870  still  remain,  and  are  finally  recognized  as  facts 
which,  for  the  sake  of  a  convenient  principle,  must  not  be 
forced  into  a  conspicuous  position.  The  behavior  of  the 
elements  of  low  atomic  weight,  the  appearance  of  one  and 
the  same  element  in  more  than  one  degree  of  oxidation, 
the  properties  of  the  platinum  metals,  either  receive  no  ex- 
pression in  the  system,  or  they  stand  in  direct  contradiction  to 
its  laws.  The  difficulties  involved,  however,  are  confined 
chiefly  to  the  compounds.  The  relations  between  the  elements, 
as  elements,  are  in  almost  every  case  clearly  pointed  out  in  the 

*  Amer.  Chem.  Jour.,  xx,  July,  1898. 


THE  PERIODIC  SYSTEM.  159 

usual  tables.  This  is  true  in  regard  to  both  the  physical  and 
chemical  properties  of  the  elements  themselves.  In  this  paper, 
therefore,  only  that  part  of  Mendele*efFs  law  will  be  discussed, 
which  says  that  the  nature  of  the  compounds  of  an  element  is 
also  a  function  of  its  atomic  weight. 

Of  the  sixty-five  elements  having  places  in  the  system,  nine 
of  them,  iron,  cobalt,  nickel,  and  the  platinum  metals,  are  put 
in  a  vertical  row  by  themselves,  where  they  form  the  so-called 
eighth  family,  a  family  which  may  be  said  to  fall  outside  the 
system  proper.  In  this  group  many  of  the  regularities  which 
can  be  traced  through  other  families  are  wanting. 

The  valency  of  the  elements  increases  by  one  in  each  suc- 
cessive vertical  row  of  the  system,  until  the  fourth  is  reached, 
after  which  each  family  yields  two  series  of  compounds,  the 
one  of  increased,  the  other  of  decreased  valency.  In  the 
potassium-nickel  series,  for  instance,  the  various  elements 
should  enter  into  compounds  with  the  valencies: 

K1,  Can,  Scm,  TiIV,  Vv,  CrVI,  Mnvn,  (F     Co,  Ki)vm. 
Vm,  Or11,  Mn1. 

So,  since  chromium  falls  within  the  sixth  family,  the  great- 
est weight  is  laid  upon  the  fact  that  chromic  acid  and  its  salts 
show  such  close  analogy  to  sulphuric  acid  and  the  sulphates. 
The  fact  that  potassium  permanganate  is  isomorphous  with 
the  perchlorate,  and  like  the  latter  only  sparingly  soluble  in 
cold  water,  likewise  assumes  the  utmost  importance.  If  com- 
pounds of  iron,  cobalt,  and  nickel  were  known,  in  which  these 
elements  were  octavalent,  they,  too,  would  possess  the  greatest 
theoretical  value.  But,  with  the  exception  of  nickel  carbonyl, 
a  doubtful  case  of  octavalency,  these  theoretically  necessary 
compounds  have  never  been  obtained.  Up  to  the  present  no 
one  has  succeeded  in  getting  beyond  the  ferric  acid  of  hexa- 
valent  iron. 

That  the  decrease  in  valency,  on  the  other  hand,  must  stop 
before  the  eighth  family  is  reached,  is  obvious,  for  the  seventh 
family  is  itself  univalent,  and  a  further  decrease  would  prevent 
iron,  cobalt,  and  nickel  from  forming  any  compounds  at  all. 


160  THE  PERIODIC  SYSTEM 

But  this  regularity  ceases  still  further  on,  —  with  chromium. 
No  univalent  manganese  compounds  have  been  obtained. 
Now,  inasmuch  as  the  iron,  cobalt,  and  nickel  compounds  fail 
to  conform  with  a  regularity  which  can  otherwise  be  traced 
throughout  the  entire  system,  they  are  assigned  an  entirely 
different  role  from  that  of  other  elements.  They  form  transi- 
tion stages,  so  to  speak,  from  the  manganous  salts  to  the 
copper  compounds  of  the  next  horizontal  row.  But  this 
transition  is  not  from  the  compounds  of  univalent  manganese 
to  those  of  univalent  copper.  Univalent  manganese  is  un- 
known. It  is  from  divalent  manganese  to  divalent  copper  — 
to  copper  in  a  degree  of  oxidation  which  in  no  way  corre- 
sponds to  the  position  of  this  element  in  the  system,  and  the 
salts  of  which  have  nothing  more  in  common  with  the  cuprous 
compounds  than  has  sulphuric  acid  with  hydrogen  sulphide ; 
the  same  element  can  be  obtained  from  both.  And  even  then 
the  road  is  by  no  means  a  smooth  one,  for  directly  before 
manganese  stands  chromium,  and  since  divalent  manganese 
has  no  place  in  the  system,  the  chromous  salts  must  be  re- 
garded as  the  true  starting-point  for  the  transition.  But  the 
transition  from  the  unstable  divalent  and  stable  trivalent  de- 
rivatives of  chromium  to  those  of  ferrous  and  ferric  iron  is 
through  a  manganese  in  which  the  relative  stability  in  the  two 
degrees  of  oxidation  is  exactly  the  reverse. 

I  know  I  lay  myself  open  here  to  the  charge  of  expecting 
too  much  from  the  system.  But  why  ?  Here  is  a  great  law 
of  nature,  the  correctness  of  which  no  one  can  doubt.  But  in 
order  to  illustrate  this  law,  an  empirical  arrangement  of  the 
elements  is  formed,  and  this  arrangement  we  are  all  too  apt  to 
confuse  with  the  law  itself.  The  periodic  system  is  satis- 
factory enough  for  the  elements.  Lothar  Meyer's  curves  of 
the  atomic  volumes  and  melting-points  prove  this.  For  the 
compounds  it  is  unsatisfactory.  And  in  order  to  find  out  how 
the  law  does  apply  to  compounds,  we  must  sift  out  and  dis- 
cuss the  discrepancies  which  the  system  shows  in  regard  to 
them. 

As  with  iron,  cobalt,  and  nickel,  so  it  is  with  all  the  other 


AND  INORGANIC  COMPOUNDS.  161 

members  of  the  eighth  group.  These  metals,  at  the  time  of 
the  promulgation  of  the  periodic  system,  were  assigned  a  posi- 
tion which,  satisfactory  though  it  was  in  illustration  of  their 
properties  as  elements,  was  in  regard  to  their  compounds  abso- 
lutely abnormal ;  and  no  amount  of  investigation  and  specula- 
tion, with  the  periodic  system  as  a  basis,  can  clear  up  the 
contradictions  which  their  position  entails. 

A  second  point  upon  which  no  light  has  been  thrown  lies 
in  the  behavior  of  the  so-called  "  typical  elements."  These, 
as  Ostwald  remarks,  instead  of  being  types  of  the  families  at 
the  head  of  which  they  stand,  have  in  the  majority  of  cases 
properties  directly  at  variance  with  those  of  the  other  mem- 
bers of  their  respective  groups.  In  his  "  Principles  of  Chem- 
istry "  Mendele'eff  says :  "  The  elements  of  the  first  two  series 
have  the  least  atomic  weights,  and  in  consequence  of  this  very 
circumstance,  although  they  bear  the  general  properties  of  a 
group,  still  they  show  many  peculiar  and  independent  proper- 
ties. These  lightest  elements  are  : 

H; 

Li,  Be,  B,  C,  N,  0,  P- 

Na,  Mg,  ..,..,.  .." 

As  Mendele'efT  left  these  elements,  "  typical,"  so  they  have 
remained,  and  the  history  of  thirty  years  contains  no  mention 
of  a  successful  attempt  to  unite  them  more  closely  than  by 
that  ill-fitting  word  to  the  groups  to  which  they  should  show 
analogies. 

Lithium  is  the  lightest  of  all  the  elements  having  places  in 
the  system.  It  should,  therefore,  from  the  above,  have  the 
greatest  number  of  independent  properties  of  any  of  the 
typical  elements.  Or,  one  should  at  least  expect  to  find  me- 
tallic lithium  and  lithium  compounds  varying  from  the  higher 
alkali  metals  and  their  derivatives  in  one  and  the  same  degree, 
since  their  departure  from  the  rest  of  the  group  is  conditioned 
by  one  and  the  same  cause.  The  abnormal  behavior  of  the 
other  typical  elements  should  be  along  the  same  lines  as  in  the 
case  of  lithium  and  its  compounds.  The  essential  properties 

11 


162  THE  PERIODIC  SYSTEM 

of  metallic  lithium  stand  in  strictest  analogy  to  those  of  the 
other  alkali  metals.  Metallic  beryllium  fits  in  accurately  in 
the  series  formed  by  magnesium,  zinc,  cadmium,  and  mercury. 
Between  boron  and  aluminium  the  analogy  is  less  clear ;  but 
it  appears  again  in  full  force  in  the  properties  of  free  carbon 
and  silicon.  The  two  elements  show,  in  their  physical  proper- 
ties, allotropic  modifications,  and  indifference  to  reagents,  the 
strongest  similarity.  Fluorine  and  chlorine,  in  the  elementary 
state,  present  the  most  striking  analogies ;  and  the  gradations 
in  character  which  the  free  halogens  undergo  with  increasing 
atomic  weight,  from  fluorine  through  to  iodine,  yield  one  of 
the  most  perfect  chemical  series  imaginable. 

Of  the  seven  elements  making  up  the  first  horizontal  row, 
therefore,  at  least  four  possess,  in  the  elementary  state,  proper- 
ties closely  akin  to  those  of  the  subsequent  elements  in  their 
respective  families,  and  complete  the  series  which  the  latter 
form. 

Now,  if  the  periodic  system  is  true  for  compounds  as  well  • 
as  for  the  elements  themselves,  then  the  compounds  of  anal- 
ogous elements  must  be  analogous,  —  a  simple  deduction  from 
the  law  which  is  not  altered  in  its  bearing  by  the  fact  that 
the  elements  with  which  we  happen  to  be  dealing  fall  within 
the  so-called  typical  class.  If  the  low  atomic  weights,  there- 
fore, of  the  four  elements  —  lithium,  beryllium,  carbon,  and 
fluorine  —  are  not  of  such  influence  as  to  prevent  their  ranking 
as  they  should  in  their  respective  families,  we  must  expect 
that  their  compounds  will  also  show  analogy  to  those  of  the 
other  members  of  their  groups.  The  compounds  of  lithium 
vary  more  or  less  from  those  of  the  other  alkali  metals,  it  is 
true ;  its  phosphate  and  carbonate,  especially,  are  less  soluble  ; 
but,  nevertheless,  the  lithium  salts  in  general  possess  the  char- 
acteristics of  alkali  derivatives,  to  an  extent  which  would  cer- 
tainly prevent  any  one  from  considering  lithium  as  anything 
but  an  alkali  metal.  Carbon  and  silicon  likewise  bear  close 
relationship  in  their  compounds.  The  property  of  carbon 
which  gives  rise  to  organic  radicals  and  the  existence  of  such 
a  multitude  of  combinations  between  but  a  few  elements,  the 


AND  INORGANIC  COMPOUNDS.  163 

ability  of  the  carbon  atoms  to  unite  with  one  another,  likewise 
appears  in  silicon.  The  silicon  hydrides,  the  various  chlo- 
rides, bromides,  and  iodides,  silicon-chloroform,  and  the  com- 
plex oxygen  compounds,  such  as  silico-oxalic  and  mesoxalic 
acids,  illustrate  fully  the  strong  similarity  between  the 
influence  of  tetravalent  carbon  and  that  of  silicon  upon  their 
compounds. 

The  law,  and  its  expression  by  the  periodic  system,  there- 
fore, holds  good  in  the  case  of  lithium  and  carbon,  and  no 
fault  can  be  found  with  the  typical  behavior  of  the  two  ele- 
ments. Now,  if  the  effect  of  small  atomic  weight  upon  both 
lithium  and  carbon  is  too  slight  to  cause  in  the  nature  of 
their  compounds  any  great  variation  from  that  of  their  homo- 
logues,  one  has  a  perfect  right  to  assume  that  this  separating 
influence  will  not  be  greater  in  an  element  which  in  its 
atomic  weight  lies  between  the  two ;  but,  after  a  comparison 
unprejudiced  by  the  fact  that  an  analogy  between  the  com- 
pounds of  beryllium  and  magnesium  is  required  by  their  posi- 
tions in  the  system,  can  a  single  trace  of  true  resemblance  be 
found  between  them,  or  between  beryllium  derivatives  and 
those  of  any  other  element  in  the  second  vertical  row?  Mag- 
nesium hydroxide  and  beryllium  hydroxide  are  both  dibasic,  it 
is  true.  But  there  the  similarity  ceases. 

A  strongly  distinctive  feature  of  all  magnesium,  zinc,  and 
cadmium  salts  is  seen  in  their  behavior  toward  ammonia  and 
ammonium  salts.  They  also  have  a  pronounced  tendency  to 
form  double  salts  with  the  compounds  of  other  metals.  Their 
oxides  are  insoluble  in  water,  but  soluble  even  in  weak  acids. 
Calcium,  strontium,  and  barium,  on  the  other  hand,  are  char- 
acterized by  their  soluble,  strongly  alkaline  hydroxides,  by 
their  difficultly  soluble  sulphates,  and  by  the  difficulty  with 
which  they  enter  into  double  salts.  These  are  group  charac- 
teristics, the  presence  of  any  one  of  which  indicates  the 
others.  They  give  a  tone  to,  and  define  the  nature  of,  all  the 
compounds  of  the  two  series.  But  to  beryllium  salts  not  one 
of  them  applies.  Similar  to  magnesium  though  the  metal  be, 
its  compounds  show  perfect  indifference  to  ammonium  salts  ; 


164  THE  PERIODIC  SYSTEM 

they  form  no  double  salts,*  and  the  oxide  is  practically  insol- 
uble even  in  strong,  hot  acids;  as  little  soluble,  in  fact,  as 
alumina.  This  last  fact,  together  with  the  ready  solubility  of 
the  sulphate  and  of  the  fluoride,  and  the  insolubility  of  the 
sulphide,  etc.,  prevent  any  comparison  of  the  beryllium  com- 
pounds with  those  of  the  alkaline  earths. 

With  fluorine,  the  nature  of  the  compounds  of  which  it  will 
be  unnecessary  to  discuss  in  full,  the  case  is  similar,  although 
its  atomic  weight  is  nearly  three  times  as  great  as  that  of 
lithium.  The  properties  of  the  free  element  show  it  to  be 
a  pronounced  halogen,  with  characteristics  which  one  would 
expect  to  find  in  a  halogen  of  lower  atomic  weight  than  chlo- 
rine. But  its  compounds  are  not  only  widely  different  from 
those  of  chlorine,  but  they  often  vary  in  a  direction  contrary 
to  that  of  the  gradations  observed  in  the  rest  of  the  series. 
Fluorine,  it  is  true,  forms  in  common  with  the  other  halogens 
an  acid  of  the  type  HR.  But  in  distinction  from  hydro- 
chloric, hydrobromic,  and  hydriodic  acid,  hydrofluoric  acid  has 
a  remarkably  low  molecular  conductivity  ;  and  its  salts,  in  the 
majority  of  cases,  have  properties  which  are  directly  the  oppo- 
site of  those  of  the  chlorides,  bromides,  and  iodides.  The 
most  pronounced  chemical  characteristic  of  the  halogen  acids 
certainly  lies  in  the  solubility  of  their  salts  with  heavy  metals, 
and  the  insolubility  of  the  silver,  cuprous,  and  mercurous  com- 
pounds. The  fluorides  of  silver  and  mercury,  on  the  other 
hand,  are  readily  soluble  :  those  of  calcium,  strontium,  barium, 
magnesium,  manganese,  iron,  cobalt,  nickel,  chromium,  cad- 
mium, copper,  bismuth,  lead,  and  others,  are  either  sparingly 
soluble,  or  dissolve  only  in  an  excess  of  hydrofluoric  acid.  In 
the  readiness  with  which  fluorine  enters  into  metallofluoric 
acids  is  seen  another  great  distinction  from  the  other  halogens. 
In  this,  as  in  many  of  its  other  properties,  it  approaches  very 
closely  to  cyanogen.  Hydrofluoric  and  hydrocyanic  acids  and 

*  Certain  double  fluorides  must  be  noted  as  exceptions  to  this  statement. 
The  double  sulphates,  phosphates,  etc.,  known,  may  be  disregarded,  as  they 
can  be  represented  by  simple  constitutional  formulas,  and  this  formation  is 
of  less  significance  than  that  of  double  halogenides  and  the  like.  Both 
calcium  and  strontium  yield  double  sulphates. 


AND  INORGANIC  COMPOUNDS.  165 

their  salts  have,  in  fact,  little  more  in  common  with  hydro- 
chloric, hydrobromic,  hydriodic  acids,  and  the  halides,  than 
the  fact  that  they  are  monobasic  or  derivatives  of  monobasic 
acids. 

We  have,  therefore,  in  lithium,  beryllium,  carbon,  and 
fluorine,  four  typical  elements  which  in  the  free  state,  as  ele- 
ments, stand  in  close  relationship  to  the  other  elements  of 
their  respective  groups.  In  two  of  them,  lithium  and  carbon, 
the  influence  of  their  low  atomic  weights  is  not  such  as  to 
deprive  their  compounds  of  the  chemical  nature  which  charac- 
terizes the  derivatives  of  their  analogues.  The  others,  al- 
though one  of  them  lies  between  lithium  and  carbon,  and  the 
other  has  an  atomic  weight  almost  large  enough  to  take  it 
out  of  the  typical  class,  fail  to  show  analogy  to  their  homo- 
logues ;  that  is,  to  satisfy  the  requirements  of  the  system,  as 
soon  as  they  pass  from  the  free  state  into  combination. 

These  are  contradictions  which  even  the  mysterious  influence 
of  a  low  atomic  weight  will  not  explain.  They  were  known 
in  1870,  and  they  stand  to-day.  With  the  development  of 
organic  chemistry,  and  the  increase  in  the  number  of  bodies 
known,  which  could  not  be  explained  by  the  laws  of  valency 
alone,  stereochemistry  appeared.  Molecular  compounds  have 
been  the  subject  of  numerous  theories,  of  which  one  at  least, 
that  of  Werner,  promises  to  bear  fruit ;  but  the  inconsis- 
tencies shown,  in  reference  to  the  other  elements,  by  those  of 
low  atomic  weight,  the  exceptions  to  a  law  more  far-reaching 
than  that  of  valency  itself,  have  remained  untouched,  simply 
in  recognition  of  the  fact  that  it  was  hopeless  to  look  for  any 
explanation  for  them  which  could  be  reconciled  to  the  system. 
And  why  ?  Because  the  inorganic  chemist,  in  standing  upon 
the  periodic  system,  has  been  unable  to  dissociate  in  his  mind 
the  chemical  compound  from  the  elements  of  which  its  formula 
contains  the  symbols. 

Of  the  work  done  in  the  development  of  group  analogies, 
little  need  be  said.  This  has  been  the  only  successful  field  of 
investigation  which  the  formulation  of  the  system  opened. 
But  it  may  be  well  to  point  out  briefly  certain  inconsistencies 


166  THE  PERIODIC  SYSTEM 

which  are  involved  in  the  development  of  these  analogies 
between  neighboring  metals  in  the  horizontal  rows. 

One  of  the  pronounced  features  of  the  periodic  system  is 
the  regularity  with  which  the  valency  of  the  elements  increases 
in  the  successive  vertical  rows,  —  a  regularity  to  which,  in  fact, 
so  much  importance  is  attached  that  Mendele*eff  can  say  with- 
out fear  of  criticism,  "  PbO2  is  the  normal  salt-forming  oxide 
of  lead,  as  are  Bi2O6,  CeO2,  TeO8  of  bismuth,  cerium,  and 
tellurium  I "  According  to  Mendele'eff,  when  an  element 
forms  two  series  of  compounds,  as  copper,  for  instance,  in  one 
of  which  it  has  the  same  valency  as  its  neighbor  in  the  hori- 
zontal row,  its  compounds  in  this  degree  of  oxidation  must  be 
similar  to  those  of  its  neighbor.  This  rule  is  well  illustrated 
in  the  case  of  copper,  for  the  cupric  compounds  do  bear  a  very 
close  resemblance  to  those  of  the  next  element,  zinc.  But 
examine  the  rule  in  its  full  extension.  The  formation  of  an 
alum  by  any  trivalent  metal  is  rightly  regarded  as  character- 
izing its  behavior  throughout  all  its  compounds  in  this  degree 
of  oxidation,  and  sharply  distinguishes  its  sesquioxide  from 
those  of  another  great  class  of  elements,  the  rare-earth  metals. 
Associated  with  the  formation  of  alums  is  the  behavior  of  the 
cyanides  toward  potassium  cyanide.  All  the  sesquioxides  * 
which  form  alums  yield  soluble  double  potassium  cyanides, 
the  great  majority  of  which  have  the  formula  K3M(CN)6. 

In  the  series, 

K,  Ca,  Sc,  Ti,  V,  Cr,  Mn,  Fe,  Co,  Ni, 

the  most  typical  double  cyanide  is  formed  by  iron;  that  of 
cobalt  is  also  stable,  and  on  the  other  side  we  find  an  analo- 
gous salt  formed  by  manganese,  "  owing  to  its  proximity  to 
iron."  But  chromium,  beyond  manganese,  also  forms  one ;  and 
from  some  experiments  which  I  myself  have  made,  I  find  also 
that  potassium  vanadicyanide,  K8V(CN)6,  is  not  only  capable 
of  existence,  but  a  well-defined  compound.  We  have  here  the 
character  which  the  atomic  weight  56  lends  to  the  compounds 

*  The  only  exception  is  in  the  case  of  aluminium,  the  cyanide  of  which  is 
decomposed  by  water.  Potassium  cyanide  precipitates  the  hydroxide. 


AND  INORGANIC  COMPOUNDS.  167 

of  trivalent  iron  exerting  an  influence  upon  that  of  one  ele- 
ment to  the  right  and  three  elements  to  the  left.  With  the 
alums  the  case  is  still  more  remarkable.  These  bodies  are 
formed  by  cobalt,  iron,  manganese,  chromium,  vanadium,  and 
titanium ;  or  by  six  of  the  ten  elements  in  the  row.  And  not 
only  that;  scandium,  the  metal  next  to  titanium,  not  only 
forms  a  sesquioxide,  but  this  is  its  only  degree  of  oxidation. 
Its  compounds,  however,  have  the  properties  characteristic, 
not  of  ferric  and  aluminium  salts,  but  of  the  rare  earths. 
And,  nevertheless,  the  close  proximity  of  this  element  to 
titanium  does  not  lend  to  the  trivalent  compounds  of  the 
latter  a  single  one  of  the  properties  of  the  rare  earths.  We 
must  seek  the  influence  to  which  the  character  of  the  titanous 
salts  is  due  far  over  at  the  edge  of  the  table. 

In  the  foregoing  pages  no  attempt  has  been  made  to  criti- 
cise the  analogies  which  exist,  in  the  various  series,  between 
the  elements  themselves.  With  this  feature  of  the  system 
little  fault  can  be  found.  The  alkali  metals,  the  alkaline 
earth  metals,  Be,  Mg,  Zn,  .  .,  Ge,  Sn,  Pb,  are  thoroughly 
similar  among  themselves,  and  well  illustrate  the  gradation  in 
properties  with  increasing  atomic  weight.  But  with  the  com- 
pounds the  case  is  entirely  different.  The  derivatives  of 
typical  elements  show  no  regularity  —  even  in  their  abnormal 
behavior;  the  compounds  of  the  eighth  group  have  a  decidedly 
anomalous  position.  The  similarity  between  the  derivatives 
of  elements  in  states  of  oxidation  uncalled  for  by  the  system, 
either  cannot  be  explained  at  all,  as  in  the  case  of  lead  and 
barium,  magnesium  and  manganese  compounds,  or  we  are 
forced  to  ascribe  to  one  or  the  other  series  a  certain  vague, 
transitive  nature.  The  reason  for  this  lies,  not  in  the  principle 
that  the  chemical  nature  of  an  element  and  its  compounds  is 
a  function  of  its  atomic  weight,  but  in  our  failure  to  recognize 
the  twofold  character  of  this  principle.  We  attempt  to  apply 
one  and  the  same  expression  of  the  law  to  both  elements  and 
compounds.  But  one  has  no  right,  in  the  systematization  of 
one  class  of  substances,  to  impose  upon  himself  restrictions 
which  arise  only  from  the  system  which  he  employs  for 


168  THE  PERIODIC  SYSTEM 

another  class.  No  arrangement  of  the  elements  according  to 
their  atomic  weights  can  be  made,  which  expresses  the  anal- 
ogies between  the  elements  themselves,  and  in  which,  for 
instance,  magnesium  and  manganese  receive  analogous  posi- 
tions. And  the  result  is  that,  in  order  to  emphasize  the 
relation  between  zinc  and  magnesium,  which  such  an  arrange- 
ment does  exhibit,  the  adherent  of  the  periodic  system  de- 
liberately closes  the  door  to  an  explanation  of  the  far  closer 
analogy  between  the  compounds  of  magnesium  and  manganese, 
as  if  the  latter  were  not  conditioned  by  an  equally  important 
law  of  nature. 

A  system  for  the  compounds,  founded  upon  the  atomic 
weights  of  the  elements,  must  also  necessarily  lead  to  confusion 
from  another  source,  for  the  investigation  of  the  compounds  is 
undertaken  solely  to  characterize  the  general  chemical  nature  of 
the  element.  Thus,  little  distinction  is  drawn  between  reac- 
tions which  do  not  involve  a  change  in  degree  of  oxidation  and 
those  which  do.  If  the  two  are  separated  at  all,  it  is  only 
when  the  resulting  compounds  are  very  stable,  or  else  con- 
form to  the  position  of  the  element  in  the  periodic  system. 
To  cuprous  compounds,  though  they  are  unstable,  great  im- 
portance is  attached,  because  copper  belongs  to  the  first  family. 
But,  even  in  so  full  and  scientific  a  text-book  as  that  of  Men- 
dele*  eft,  the  salts  of  trivalent  manganese  are  reviewed  with  lit- 
tle more  than  the  passing  remark  that  they  somewhat  resemble 
ferric  compounds,  and  that  the  chloride  decomposes  when  its 
solution  is  warmed.  The  latter  fact  seems  to  deprive  the  man- 
ganic salts  of  all  theoretical  interest. 

But  in  a  comparison  between  the  derivatives  of  two  metals 
in  the  same  degree  of  oxidation,  the  question  of  existence  be- 
comes of  more  importance  than  stability,  for  the  latter  is  often 
dependent  entirely  upon  external  conditions.  The  fact  that 
bromine  is  liquid,  iodine  a  solid,  at  ordinary  temperatures, 
does  not  prevent  the  most  important  analogies  being  drawn 
between  the  physical  properties  of  the  halogens  in  the  same 
state  of  aggregation,  though  to  obtain  bromine  and  iodine  as 
gases,  heat  must  be  employed.  So  it  is,  with  many  compounds. 


OF  THE 

UNIVERSITY 

Ov,          °F 

a^/J/.  /trr»r. 


AND  INORGANIC  COMPOUNDS.  169 

They  may  perhaps  be  obtained  only  under,  for  us,  extraordi- 
nary conditions,  but  their  very  existence  may  point  out  in  the 
constituent  elements  properties  which  we  should  otherwise 
never  expect.  As  an  example  of  such  a  case  only  the  newly 
discovered  alums  of  vanadium  need  be  mentioned.  The  exist- 
ence of  these  bodies  shows  that  in  spite  of  the  similarity  be- 
tween phosphates  and  vanadates,  the  vanadium  atom  exerts 
upon  the  nature  of  its  trivalent  compounds  the  same  influence 
as  does  iron  upon  that  of  the  ferric  salts.  A  vanadic  solution 
absorbs  oxygen  with  great  avidity,  and  is  therefore  called  very 
unstable,  but  the  presence  of  oxygen  is  an  arbitrarily  imposed 
condition.  If  oxygen  were  a  rare  element,  the  trivalent  salts 
of  vanadium  would  probably  be  regarded  as  its  normal  com- 
pounds, and  a  vanadate  looked  upon  very  much  as  we  look 
upon  ferric  acid  to-day. 

The  chemical  behavior  of  an  element  in  a  given  degree  of 
oxidation  must  be  characterized  along  two  lines.  First,  by  the 
study  of  its  compounds  as  mineralogical  specimens,  their  com- 
position, physical  properties,  solubility,  volatility,  and  the  like, 
together  with  the  reactions  which  they  show  without  involv- 
ing change  in  the  degree  of  oxidation.  Secondly,  by  its  pas- 
sage from  this  degree  of  oxidation  into  others.  The  first  is, 
in  my  opinion,  by  far  the  more  important,  for  the  properties  of 
the  compounds  of  an  element  in  two  different  degrees  of  oxida- 
tion differ  absolutely  from  one  another;  and  in  the  two  the 
element  appears  in  entirely  different  r61es.  It  is  only  after  we 
have  ascertained  in  how  far  the  element  can  alter  its  apparent 
character,  in  corresponding  with  entirely  different  elements  in 
different  degrees  of  oxidation,  that  we  can  solve  its  true  char- 
acter and  find  out  a  general  law  for  its  behavior  in  all  its 
compounds;  and  this  can  be  ascertained  only  by  a  careful 
comparison  of  its  compounds  with  those  of  other  elements 
in  the  same  degree  of  oxidation. 

A  classification  based  upon  this  principle,  of  course,  presents 
great  difficulties,  owing  to  the  very  unsatisfactory  extent  to 
which  the  elements  in  their  unstable  degrees  of  oxidation  have 
been  investigated.  A  thorough  study  of  the  compounds,  how- 


170  THE  PERIODIC  SYSTEM 

ever,  has  shown  that  it  is  capable  of  giving  most  interesting 
results. 

II.    GRADATIONS  IN  THE  PROPERTIES  OF  ALUMS.* 

In  my  first  paper  on  this  subject,  f  I  attempted  to  show 
that  the  well-known  difficulties  which  confront  the  chemist  in 
classifying  the  elements  and  their  compounds  according  to  the 
Periodic  System  are  confined  practically  to  the  latter  class  of 
substances.  That  there  is  a  definite  connection  between  the 
properties  of  an  element  and  those  of  its  compounds  is  of 
course  obvious,  from  the  numerous  cases  in  which  both  fulfil 
the  requirements  of  the  system.  But,  to  take  one  of  the  chief 
difficulties,  there  are  almost  no  instances  in  which,  when  an 
element  can  appear  in  more  than  one  degree  of  oxidation,  the 
properties  of  its  compounds  in  each  type  find  accurate  inter- 
pretation by  the  System.  As  a  case  in  point  may  be  cited  ni- 
tric acid,  the  nitrates,  and  nitrous  acid  and  the  nitrites,  as 
compared  respectively  with  the  derivatives  of  the  pentoxide 
and  trioxide  of  phosphorus.  So  far  as  their  oxygen  compounds 
are  concerned,  the  two  elements  have  in  neither  the  quini- 
valent  nor  trivalent  state  anything  in  common,  except  their 
valence  and  acid-forming  nature.  In  crystallographic  form, 
solubility,  even  in  formulas,  their  derivatives  are  inherently 
different.  Nitrogen  pentoxide  is  a  volatile  liquid ;  phospho- 
rus pentoxide  a  non-volatile  solid.  The  former  forms  only  the 
monobasic  acid  HNO8;  the  latter  yields  preferably  polybasic 
acids ;  the  normal  nitrates  are  in  every  case  readily  soluble  in 
water :  the  normal  phosphates,  pyrophosphates,  and  metaphos- 
phates  are  in  almost  every  case  insoluble  in  water. 

With  the  trioxides  the  degree  of  similarity  is  about  the 
same ;  strict  analogy  is  practically  absent.  But  nevertheless 
such  a  loose  periodic-system  worship  prevails,  that  almost 
every  modern  text-book  on  inorganic  chemistry  contains  a 
stereotyped  statement  that  nitric  acid  is  analogous  to  phos- 
phoric acid.  In  some  instances  even  these  bounds  have  been 

*  Amer.  Chem.  Jour.,  xxvi,  August,  1901.  t  Ibid.,  xx,  581. 


AND  INORGANIC  COMPOUNDS.  171 

far  overstepped.  Probably  the  most  thoroughly  systematized 
smaller  work  on  the  subject  is  that  of  Professor  Ramsay.  On 
pp.  333  ff.  of  his  "System  of  Inorganic  Chemistry"  (1891), 
he  classes  nitrogen  tetroxide  with  vanadium  tetroxide,  nitrous 
acid,  and  with  vanadious  hydroxide.  The  latter  two  are  ap- 
parently analogous  because  they  have  the  analogous  formulas 
NO(OH)  and  VO(OH).  If  this  is  enough  for  chemical  anal- 
ogy, why  should  not  the  aluminium  compound,  AIO(OH),  be 
put  in  the  same  class  ?  Aluminium  and  vanadium  both  form 
alums,  and,  as  he  emphasizes  of  vanadium  hydroxide,  both 
unite  with  the  alkalies.  I  speak  of  this,  not  in  criticism  of 
Professor  Ramsay's  book,  but  in  protest  against  the  all-prevail- 
ing tendency  to  go  a-begging  for  chemical  analogy  when  the 
system  requires  it. 

The  term  "  chemical  character  of  an  element "  has  two  very 
different  meanings.  In  the  first  place  it  denotes  the  behavior 
of  the  element  itself,  in  the  free  state ;  in  the  second,  the  type 
of  reactions  of  its  compounds.  In  the  latter  case  we  may 
perhaps  use  an  explanatory  prefix,  and  say,  for  instance,  "  the 
character  of  ferric  iron  "  or  of  "ferrous  iron."  The  two  terms 
denote  two  absolutely  different  states  of  matter.  When  one 
speaks  of  ferric  iron,  the  mind  involuntarily  associates  it,  not 
with  ferrous  iron,  nor  metallic  iron,  but  with  the  salts  of 
aluminium  and  trivalent  chromium ;  with  two  elements  which 
in  the  free  state  bear  no  analogy  to  metallic  iron,*  and  no.  rela- 
tion between  which  and  iron  is  shown  by  the  System.  The 
simplest  and  most  natural  analogues  of  ferric  iron  are  merely 
the  trivalent  ions  of  aluminium  and  chromium.  On  the  other 
hand,  "  ferrous  iron  "  brings  to  the  mind,  in  addition  to  the 
idea  of  something  readily  oxidizable,  the  thought  of  magnesium 
and  zinc  compounds,  —  derivatives  of  elements  which  again 
have  nothing  in  common  with  metallic  iron,  and  also  no  re- 
semblance to  the  metals  which  iron  in  the  trivalent  state  is 
analogous.  Unless  a  very  strong  distinction  is  made  between 

*  By  this  I  mean  the  strict  analogy  which  is  exhibited  between  free  ele- 
ments belonging  to  the  same  family  and  sub-group  in  the  System ;  for  example, 
metallic  zinc  and  cadmium,  silver  and  gold,  arsenic  and  antimony,  etc. 


172  THE  PERIODIC  SYSTEM 

the  different  usages  of  the  term  "  chemical  character  of  iron," 
therefore,  this  brings  about  a  state  of  hopeless  confusion.  Up 
to  the  present  time  it  certainly  has  led  to  a  marked  subordi- 
nation, in  importance,  of  compounds  containing  elements 
in  unstable  states  of  valence  to  those  in  which  they  are 
stable.  Practically,  this  is  all  very  well.  But  from  the 
theoretical  standpoint  it  imposes  a  direct  obstacle  in  the  way 
of  careful  and  systematic  interpretation  of  fact,  for  it  makes 
in  such  cases  the  power  of  oxidation  or  reduction  much  more 
important  than  the  simple  properties  of  the  compounds  as 
such. 

The  laws  of  electricity  cease  to  obtain,  as  soon  as  that  force 
has  been  converted  into  light,  or  heat,  or  chemical  energy  — 
no  matter  which.  But  ferric  iron  and  ferrous  iron  are  just  as 
distinct  primary  forms  of  matter  as  these  are  distinct  forms  of 
energy.  Like  the  latter,  they  may  be  converted  the  one  into 
the  other,  or  they  may  be  converted  into  metallic  iron.  But 
whether  a  ferric  salt  passes  into  a  ferrous  salt  or  into  metallic 
iron,  the  form  of  matter  analogous  to  aluminium  in  the  com- 
bined state  ceases  to  exist.  What  it  becomes,  and  how  readily 
it  undergoes  alteration,  are  questions  common  to  all  the  ferric 
compounds,  and  should  be  theoretically  regarded  as  belonging 
to  a  set  of  problems  entirely  distinct  and  separate  from  those 
involving  the  individual  salts. 

In  order  to  clearly  characterize  an  element  in  a  given  degree 
of  oxidation,  the  first  step  should  be,  not  to  ascertain  how 
stable  or  unstable  its  compounds  are,  but  how  nearly  they 
approach,  in  their  physical  properties,  solubility,  etc.,  the  cor- 
responding salts  of  other  elements  of  the  same  valence.  Such 
arbitrary  conditions  as,  for  instance,  the  presence  of  oxygen  in 
working  with  easily  oxidizable  substances,  should  be  avoided. 
And,  furthermore,  the  question  of  analogy  should  be  decided 
along  strict  lines.  The  rare-earth  metals  are,  more  often  than 
not,  spoken  of  as  analogous  to  aluminium.  But  the  two  nota- 
ble properties  which  characterize  the  aluminium  salts  —  the 
extremely  weak  basicity  of  the  hydroxide,  with  the  correspond- 
ing readiness  to  form  basic  salts;  and  the  marked  tendency 


AND  INORGANIC  COMPOUNDS.  173 

to  form  complex  ions  (still  more  highly  developed  in  chromium 
and  ferric  iron),  as  illustrated  in  the  behavior  of  aluminium 
solutions  containing  oxalic,  tartaric,  or  other  organic  acids,  are 
just  the  reverse  of  the  properties  which  characterize  the 
strongly  basic  rare-earths.  In  Dammer's  Handbuch  we  find 
specific  mention  of  fourteen  derivatives  of  aluminium  chloride. 
Under  cerous  chloride  —  the  chlorine  compound  of  the  best 
investigated  rare  earth  —  we  find  but  two.*  Barium  chloride 
and  cupric  chloride  show  a  similar  difference.  In  both  cases 
the  divergence  is  due  to  much  the  same  cause.  The  very 
nature  of  the  strongly  basic  ions  of  barium  and  cerium  pre- 
vent the  formation  of  such  derivatives ;  and  since  the  diver- 
gence in  the  behavior  of  the  chlorides  is  duplicated  in  that  of 
sulphates,  nitrates,  bromides,  and  countless  other  salts,  it 
surely  indicates  a  radical  distinction  in  the  characters  of 
cerium  and  aluminium,  to  which  much  more  weight  should  be 
attached  than  to  the  fact  that  the  hydroxides  of  both  are 
flocculent  precipitates.  The  latter  resemblance  is  essentially 
the  basis  of  assertions  that  they  are  analogous.  Cerium  may 
be  regarded  as  the  prototype  of  the  rare-earth  metals ;  alumin- 
ium as  that  of  trivalent  chromium,  manganese,  vanadium,  iron, 
cobalt,  and  others.  In  each  group  the  reactions  of  these  typi- 
cal metals  are  closely  followed  by  all  their  respective  mem- 
bers, in  a  way  which  proves  that  the  separate  reactions  of  each 
are  not  to  be  regarded  as  individual  functions  of  the  elements, 
but  closely  correlated  with  one  another.  For  instance,  it 
means  that  a  trivalent  metal  which  forms  alums  will  yield 
complex  tartrate  ions ;  and  that  a  trivalent  metal  which  has  a 
strongly  basic  hydroxide  will  form  an  insoluble  oxalate,  and 
not  form  an  aluin  nor  a  double  chloride  with  potassium  chlo- 
ride ;  but  that  its  oxide  will  dissolve  readily  in  dilute  acids. 
As  illustrations  in  the  above,  I  have  chosen  the  trivalent 
metals  by  chance.  Others  would  have  done  just  as  well.  If 
we  compare  the  solubility  relations  and,  exclusive  of  those  in 
which  a  change  of  valence  takes  place,  the  reactions,  of  cu- 
prous compounds,  with  those  of  the  corresponding  silver  salts, 

*  Exclusive  of  the  platinichloride,  etc. 


174  THE  PERIODIC  SYSTEM 

we  find  an  almost  exact  similarity  between  the  two.  But  to 
ascertain  experimentally  in  how  far  the  strict  classification  of 
the  elements  in  the  manner  indicated  is  possible,  the  trivalent 
metals  are  especially  suitable.  Among  the  alum-forming  ele- 
ments we  find  one  (cobalt)  which  in  the  trivalent  state  yields 
compounds  that  are  very  unstable  because  of  the  high  valence ; 
and  a  second  one  (vanadium)  whose  compounds  are  equally 
unstable  because  of  the  abnormally  low  valence.  The  range 
of  atomic  weights  of  the  alum-forming  trivalent  metals,  from 
27  (Al.)  to  114  (In.)  is  also  exceptionally  great  for  an  iso- 
morphous  series,  and  these  elements  constitute  members  of 
six  out  of  the  eight  families  in  the  System. 

The  total  number  of  trivalent  elements  entering  into  the 
compounds  M1  Mra  (SO4)2.12H2O,  is  nine,  —  aluminium,  tita- 
nium, vanadium,  chromium,  manganese,  iron,  cobalt,  gal- 
lium, and  indium.  Of  univalent  elements,  M1  represents  five : 
sodium,  potassium,  rubidium,  caesium,  thallium ;  and  also  the 
ammonium,  hydroxylammonium,  methylammonium,  etc.,  radi- 
cals.* A  cursory  glance  over  the  literature  shows  at  once  that 
there  is  a  more  or  less  pronounced  decrease  in  stability  with 
increasing  atomic  weight  of  the  trivalent  metal  in  an  alum,  and 
apparently  that  the  heavier  the  univalent  metal,  the  greater  will 
be  the  stability.  Thus,  sodium  enters  into  alums  only  with 
the  lightest  of  the  trivalent  metals,  aluminium,  vanadium,  and 
chromium.  The  only  stable  potassium  alums  are  those  of 
aluminium  and  chromium :  potassium  ferric  and  gallium  alums 
break  down  into  basic  salts  very  readily,  and  the  only  double 
sulphates  of  potassium  and  indium  which  can  be  obtained  have 
the  formulas  Kin  (SO4)2.4H2O  and  K2SO4.2In2(SO4)3. 6H2O. 

The  only  alums  which  have  as  yet  been  obtained  of  tita- 
nium are  those  in  which  the  univalent  metal  is  caesium  or 
rubidium.!  After  much  doubt  had  been  cast  upon  the  exist- 

*  The  existence  of  the  silver  aluminium  alum  described  by  Church  and 
Northcote  is  denied  by  Retgers. 

t  Piccini,  Zeitschr.  fiir  anorg.  Chemie,  xvii,  355.  I  have  obtained  indica- 
tions of  the  existence  of  that  of  potassium. 


AND  INORGANIC   COMPOUNDS.  175 

ence  of  the  manganese  alums  described  by  Mitscherlich,  Piccini 
has  shown  that  at  least  the  csesium  compound  of  this  element 
can  be  easily  obtained.*  Owing  to  the  great  instability  of 
their  salts,  and  the  correspondingly  slight  value  which  could 
be  attached  to  measurements  of  their  physical  constants,  I 
have  felt  it  useless  to  include  these  metals  in  the  present 
investigation,  which  covers,  however,  alums  of  all  the  other 
trivalent  metals  mentioned  above,  except  gallium. 

I  have  also  rejected  the  salts  of  the  substituted  amines,  as 
involving  the  ulterior  question  of  the  influence  of  complex 
ra/licals.  The  ammonium  alums,  however,  in  view  of  their 
frequent  occurrence,  have  been  carefully  studied,  in  order  to 
ascertain  how  far  the  generally  greater  readiness  of  this  com- 
plex to  yield  double  salts,  as  compared  with  that  of  potassium, 
is  capable  of  exact  determination.  The  univalent  groups 
studied,  therefore,  were  sodium,  potassium,  ammonium,  ru- 
bidium, csesium,  and  thallium.  For  the  necessary  rubidium 
and  csesium  material  I  am  indebted  to  the  kindness  of  Prof. 
H.  L.  Wells,  who  kindly  placed  some  very  pure  compounds 
of  these  metals  at  my  disposal.  The  salts  given  in  the  follow- 
ing table  were  investigated. 

Al=:27.  V  =  51.1.  Cr  :r:  52.1.          Fe  =  66.          Co  =  59.      In  —  113. 

23          ISTa  .  .  Na  

39          K  K  K  K 

NH4  NH4  NH4  NH4 

85          Kb  Kb  Kb  Rb          Kb          Kb 

133          Cs  Cs  Cs  Cs  Cs  Cs 

204          Tl  Tl  Tl  Tl 

Solubility  in  Water  at  25°.  —  As  a  criterion  of  the  properties 
of  these  compounds,  their  solubility  in  water  at  25°  was  first 
determined.  The  literature  contains  data  only  upon  the  solu- 
bility of  the  compounds  of  aluminium  f  and  vanadium,  J  and 
all  those  given  seem  to  be  of  more  or  less  doubtful  character, 

*  Zeitschr.  f iir  anorg.  Chemie,  xvii,  355 ;  xx,  12. 

t  Poggiale,  A.,  ch.  (3),  viii,  467;  Setterberg,  Liebig's  Annalen,  ccxi,  100; 
Mulder,  Scheidekund,  Verhandl,  1864,  91 ;  etc. 
t  Piccini,  Zeitschr.  fur  anorg.  Chemie,  xiii,  441. 


176  THE  PERIODIC  SYSTEM 

the  results  having  in  each  case  been  obtained  without  the  use 
of  a  thermostat.  In  addition  to  this  fact,  the  actual  temper- 
atures chosen  by  different  experimenters  for  their  determina- 
tions were  rarely  identical;  so  that  their  results  for  a  given 
degree  would  have  to  be  calculated  by  interpolation.  I  have 
accordingly  been  forced  to  make  new  measurements  in  each 
case. 

The  determinations  were  made  in  two-ounce  bottles,  con- 
taining water  and  the  finely  divided  salts  in  excess.  These 
were  placed  in  a  digesting  bath  as  described  by  Noyes,*  and 
rapidly  shaken  by  means  of  a  turbine  for  from  four  to  six 
hours.  The  bottles  were  then  placed  upright  in  the  bath, 
and  the  suspended  salts  allowed  to  settle  for  two  hours.  The 
temperature  of  the  bath  was  controlled  by  a  gas  regulator,  and 
its  variation,  in  the  determinations  used  below,  never  exceeded 
0.2°.  From  three  to  eight  cubic  centimeters  of  the  superna- 
tant solutions  were  then  transferred  by  means  of  a  pipette,  the 
bulb  of  which  had  been  warmed,  to  small  weighing-glasses, 
weighed,  and  evaporated  to  dryness.  The  amounts  of  the  dis- 
solved salts  were  then  determined  by  heating  for  four  hours 
at  200°,  at  which  temperature  they  became  fully  dehydrated. 
The  accuracy  of  this  method  was  first  ascertained  by  experi- 
ments made  with  a  variety  of  alums.  In  these  a  weighed 
quantity  of  the  salt  was  dissolved  in  a  few  cubic*  centimeters 
of  water,  evaporated  to  dryness,  and  heated  to  constant  weight. 
The  water  was  added  to  ascertain  whether  an  error  would  be 
introduced  through  basic  salt  formation.  The  following  are 
some  of  these  determinations : 

0.4513  g.  CsCr(S04)2.12H20  gave  0.2858  g.  anhydrous  salt, 

calculated  0.2869  g. 
0.3540  g.  CsFe(S04)2.12H20  gave  0.2262  g.  anhydrous  salt, 

calculated  0.2259  g. 
0.2264  g.  CsAl(S04)2.12H20  gave  0.1411  g.  anhydrous  salt, 

calculated  0.1403  g. 
0.7814  g.  TlCr(S04)2.12H20  gave  0.5473  g.  anhydrous  salt, 

calculated  0.5474  g. 

*  Zeitschr.  fur  physikal.  Chemie,  ix,  606. 


AND  INORGANIC  COMPOUNDS.  177 

The  solubility  determination  of  the  vanadium  alums  re- 
quired great  caution,  owing  to  the  readiness  with  which  they 
undergo  oxidation.  These  salts,  which  were  made  according 
to  Piccini's  directions,*  by  electrolysis,  were  washed  by  decan- 
tation  with  boiled  water  containing  carbonic  acid,  in  ttfe  vessel 
in  which  they  had  been  crystallized ;  and  were  then  brought 
directly  into  the  bottles,  without  having  been  exposed  to  the 
air  for  an  appreciable  length  of  time.  The  water  used  for 
their  solution  had  previously  been  boiled,  and  carbon  dioxide 
led  through  it  in  the  bottles.  The  resulting  solutions  were  in 
this  case  analyzed  by  the  titration  of  weighed  quantities 
according  to  Browning's  method,  f  The  alums  of  cobalt,  of 
which  only  the  potassium  and  ammonium  compounds  had  been 
described  hitherto,  J  unfortunately  decompose  quite  rapidly  in 
solution,  giving  off  oxygen,  and  determinations  could  therefore 
not  be  made  with  them.  My  supply  of  indium,  also,  was  too 
small  to  permit  a  determination  of  any  but  its  caesium  alum. 
The  results  obtained  with  this  compound  alone,  however,  suffi- 
ciently indicate  the  role  of  indium  as  an  alum-forming  element.- 

The  results  given  below  are  in  about  half  the  cases  averages 
of  two  or  more  closely  agreeing  determinations,  and  are  chosen 
from  the  total  number  made  as  having  been  obtained  under 
the  most  perfect  conditions  of  temperature,  etc.  The  values 
refer  to  the  number  of  parts  of  salt  dissolved  in  one  liter  of 
water,  and  in  the  successive  tables  M1  represents  the  univa- 
lent  metals  contained  in  the  alums  of  the  trivalent  metal  Mm. 

Mm  =  Aluminium,  At.  wt.  =  27. 

M1  Na  K          NH4         Tl         Kb       Cs 

Anhydrous  salt,        .  .  72.3         91.9       75.0      18.1      4.7 

Hydrated  salt,          .  .  138.4       191.9      117.8      31.5      7.6 

Mra  =  Vanadium,  At.  wt.  =  51.1. 

M1         =         Na  K          NH4        Tl         Kb      Cs  § 

Anhydrous  salt,       .  .  .  .          316.9     256.0      57.9      7.71 

Hydrated  salt,         .  .  785.0     433.1      99.3    13.10 

*  Zeitschr.  fur  anorg.  Chemie,  xi,  106. 

t  Ibid.,  i,  158.  $  Soc.  Edinburgh,  lix,  760. 

§  Piccini  obtains  the  same  order  for  the  solubility  of  the  vanadium  alums 

12 


178  THE  PERIODIC  SYSTEM 

Mra  =  Chromium,  At.  wt.  =  52.1. 

M1         =         Na  K          NH4         Tl          Kb       Cs 

Anhydrous  salt,       .  .  125.1       107.8      104.8      25.67    5.7 

Hydrated  salt,          .  .  243.9       212.1      163.8      43.40     9.4 

Mm  =  Iron,  At.  wt.  =  56. 

M1         =         Na             K          NH4  Tl  Eb  Cs 

Anhydrous  salt,  Does  not  Basic  salt   441.5  361.5  97.4  17.1 

exist.      separated. 

Hydrated  salt,                                      1244.  646.0  169.8  27.2 

Mm  =  Indium,  At.  wt.  =  114. 

M1                     Na  K          NH4         Tl         Eb  Cs 

Anhydrous  salt,  Does  not  Does  not     .  .           .  .          .  .  75.7 

exist.  exist. 

Hydrated  salt,                                          117.3 

The  sodium  alums  known  dissolve  in  much  less  than  their 
own  weight  of  water,  and  were  therefore  unsuitable  for  exact 
determinations.  A  sodium  alum  of  iron  could  not  be  obtained. 
With  regard  to  the  effect  of  the  univalent  metals  upon  the 
solubility,  it  is  seen  that  the  higher  the  atomic  weight  of  an 
alkali-metal,  the  less  soluble  is  its  alum  with  any  given  triva- 
lent  metal.  The  solubilities  of  the  ammonium  and  thallium 
compounds,  however,  lie  between  those  of  the  corresponding 
salts  of  potassium  and  rubidium.  The  salt  NH4A1(SO4)2. 
12H2O  forms  the  only  exception  to  this  rule.  It  is  some- 
what more  soluble  than  KA1(SO4)2.12H2O.*  The  thallium 
alums,  furthermore,  are  in  each  case  somewhat  less  soluble 
than  those  of  ammonium. 

The  key  to  the  effect  of  the  trivalent  elements  upon  the 

at  10°.    Expressed  in  parts  by  weight  of  the  salts  dissolved  in  100  parts  water, 
his  determinations  are  as  follows : 

V— K  V— NH4  V— Tl  V— Rb  V— Cs 

198.4  39.76  11.06  2.56  0.464 

*  In  Poggiale's  determinations,  this  ammonium  alum  was  found  to  be  less 
soluble  than  the  potassium  salt.  His  results  for  the  latter  correspond  almost 
exactly  with  mine  for  the  ammonium  salt,  and  those  for  the  ammonium  alum 
with  mine  for  that  of  potassium.  It  is  probable  that  the  coincidence  is  due 
to  a  false  arrangement  of  his  tables. 


AND  INORGANIC   COMPOUNDS.  179 

solubility  relations  is  given  in  the  failure  of  any  beyond 
vanadium  to  form  alums  with  sodium,  and  in  the  decomposi- 
tion of  the  potassium  ferric  salt  by  water.  As  this  would 
indicate,  the  solubilities  of  the  alums  of  the  successive  trivalent 
metals  with  a  given  univalent  metal  increase  steadily  from 
aluminium  to  indium.  From  what  one  can  judge  through  the 
literature,  gallium  alums,  also,  follow  this  rule,  being,  next  to 
those  of  indium,  the  most  soluble.  The  chromium  alums 
alone  form  an  exception.  Their  behavior  will  be  touched  upon 
at  a  later  point. 

In  the  following  table  I  give  the  solubilities  of  all  the 
alums  determined,  expressed  in  gram-molecules  of  the  anhy- 
drous salts  per  liter  of  water: 

M1   =    K 

M111  =  Al        0.28 
V 

Cr        0.441 
Fe 
In 


These  results  may  be  represented  graphically  as  a  function 
either  of  the  molecular  weight  of  the  respective  alums  of 
given  trivalent  metals,  which  is  virtually  the  same  thing  as 
if  they  were  plotted  according  to  the  atomic  weights  of  the 
univalent  metals,  but  introduces  the  ammonium  salts ;  or  they 
may  be  referred  to  the  atomic  weights  of  the  trivalent  metals. 
To  show  the  influence  of  both  the  univalent  and  trivalent 
metals,  I  give  in  Figs.  I.  and  II.  the  results  obtained  by  each 
method.  In  Fig.  I.  the  solubilities  are  plotted  as  functions 
of  the  molecular  weights,  the  univalent  metal  being  the 
variable. 

As  is  seen,  the  curves  are  in  general  of  the  same  nature, 
but  they  have  no  uniformity  of  position,  and  render  no 
gradation  in  the  solubilities  of  the  alums  visible.  This  is  true 
whether  we  include  the  ammonium  salts  or  not,  or,  in  other 
words,  whether  the  solubilities  be  referred  to  the  molecular 


NH4 

Tl 

Rb 

Cs 

0.387 
1.210 

0.177 
0.573 

0.059 
0.177 

0.013 
0.0204 

0.407 

0.212 

0.078 

0.0151 

1.659 

0.799 

0.293 

0.045 
0.172 

180 


THE  PERIODIC  SYSTEM 


§ 


weights  or  to  the  atomic  weights  of  the  univalent  metals. 
The  only  influence  which  the  univalent  metals  or  radicals  exert 
is  a  specific  one.  The  caesium  salts  are  in  all  cases  the  least 
soluble,  the  rubidium  salts  next,  but  the  comparatively  great 
solubility  of  the  thallous  compounds,  which,  according  to  the 


AND  INORGANIC  COMPOUNDS.  181 

gradation  observed  in  the  case  of  the  compounds  of  the  alkali 
metals  proper,  should  be  the  least  soluble  of  all,  prevents  any 
satisfactory  representation  of  the  solubilities  as  a  function  of 
the  atomic  weights  of  the  univalent  metals. 

This  specific  influence  of  the  univalent  metals  is  readily 
seen  in  Fig.  II,  in  which  the  solubilities  are  plotted  as  a  func- 
tion of  the  atomic  weights  of  the  trivalent  metals. 

As  we  pass  from  the  caesium  compounds  through  those  of 
rubidium  and  thallium  to  the  ammonium  alums,  the  difference 
in  solubility  of  the  successive  salts  of  a  given  trivalent  metal 
becomes  greater.  The  increase  is  also  the  greater,  the  heavier 
the  trivalent  metal;  the  result  being  that  while  the  caesium 
alums  of  all  the  trivalent  metals  differ  only  slightly  in  solu- 
bility, and  their  curve  has  therefore  a  nearly  horizontal  posi- 
tion, the  curves  of  the  remaining  univalent  radicals  successively 
become  more  inclined ;  *  the  whole  effect  being  somewhat  like 
that  of  an  opening  fan.  But  in  each  case  the  curves  show  a 
sharp  break  at  the  chromic  compounds ;  slight  in  the  caesium 
curve,  but  more  pronounced  with  each  successive  univalent 
metal.  Apparently,  since  the  chromic  salts  accordingly  fail 
to  fall  properly  within  the  series  of  gradations  with  increasing 
atomic  weight  of  the  trivalent  metal,  the  conclusion  might  be 
drawn  that  the  great  readiness  with  which  this  element  forms 
alums  is  in  the  actuality  an  abnormal  property.  I  believe, 
however,  that  this  is  a  very  loose  way  of  interpreting  the 
fact.  Abnormal  things  do  not  occur  in  nature.  In  the  in- 
creasing solubilities  of  the  chromic  alums  as  we  pass  from 
caesium  to  ammonium,  they  show  exactly  the  same  mutual 
relations  as  are  shown  by  the  alums  of  aluminium,  vanadium, 
or  iron.  They  are  perfectly  normal  in  everything,  except  that 
their  behavior  is  not  expressed,  like  that  of  the  other  trivalent 
metals,  by  the  atomic  weight  of  the  metal  they  contain.  And 

*  Prof.  Horace  L.  Wells  suggests  to  me  that  the  marked  difference 
shown  here  between  the  solubilities  of  the  rubidium  and  caesium  alums  of 
iron  might  have  a  practical  bearing  upon  the  technical  separation  of  ru- 
bidium and  caesium.  At  present  this  is  usually  effected  by  the  fractional 
crystallization  of  their  aluminium  alums.  By  using  the  ferric  compounds 
it  would  probably  be  much  more  perfect. 


182 


THE  PERIODIC  SYSTEM 


30 


'Weights,. 

FIGURE  II. 


51  52 


56 


this  fact  indicates  almost  positively  that  the  properties  of  the 
compounds  are  not  a  function  of  the  atomic  weight  of  the  element. 


AND  INORGANIC  COMPOUNDS.  183 

If  they  were,  chromic  alums  would  have  about  twice  their 
actual  solubility. 

I  do  not  mean  by  this  to  make  a  sweeping  denial  of  all 
analogy  shown  in  the  Periodic  System.  Whatever  the  deter- 
mining cause  of  the  properties  of  compounds  may  be,  it  is 
certainly  commensurable,  in  a  great  many  instances,  with  the 
atomic  weights.  But  our  progress  toward  the  systematization 
of  the  compounds  will  be  slow  indeed,  if  we  refuse  to  recog- 
nize that  Mendele'efFs  law  is  but  a  slight  approximation  of  the 
truth.  The  abnormal  behavior  of  the  thallium  alums,  accord- 
ing to  the  Periodic  System,  might  be  conventionally  explained 
by  the  position  of  thallium  as  extraneous  to  the  first  family  of 
the  table.  But  in  the  case  of  chromium  such  an  explanation 
is  totally  inapplicable.  The  elements  aluminium,  vanadium, 
iron,  and  cobalt  *  constitute  members  of  three  different  fami- 
lies, and  nevertheless  their  alums  show  a  satisfactory  grada- 
tion according  to  the  atomic  weights  of  these  elements. 
Their  alums  are  merely  intermediate  members  in  the  series 
of  which  the  end  members,  the  aluminium,  gallium,  and  indium 
salts,  are  so  conspicuous  because  they  are  compounds  of 
three  elements  in  the  same  family  in  the  system,  and  thus 
exhibit  the  gradations  required  by  the  latter. 

The  chromic  alums,  the  thallous  alums,  and  the  ammonium 
alums  exhibit  in  each  case  the  same  peculiar  relations  to  one 
another  as  do  the  alums  of  their  kindred  elements  with  normal 
behavior.  In  the  case  of  the  ammonium  alums  this  is  espe- 
cially important,  for  it  shows  that  whatever  the  determining 
cause  of  the  properties  of  the  alums  may  be,  exactly  the  same 
cause  must  le  ascribed  to  the  behavior  of  the  ammonium  salts  as 
to  that  of  the  alums  containing  only  metals :  since  the  am- 
monium radical  has  no  true  atomic  weight,  therefore  the 
atomic  weight  itself  is  not  the  determining  cause  in  the  case 
of  any  alums  whatsoever. 

It  is  an  interesting  fact  that  the  molecular  volumes  of  the 
alums,  when  arranged  according  to  their  ascending  values, 

*  The  effect  of  this  element  upon  its  alums  is  shown  by  their  melting- 
points,  as  will  be  described  later. 


184 


THE  PERIODIC  SYSTEM 


bring  both  the  trivalent  and  univalent  elements  into  the  same 
order  as  do  their  solubilities.  In  the  following  tables*  the 
molecular  volumes  are  given  as  calculated  from  Soret's  deter- 
minations, with  the  double  formulas,  M2SO4,  M2(SO4)8. 24H2O 
as  the  basis  of  the  molecular  weights.  The  solubilities  are 
expressed  in  gram-molecules  per  liter. 


Mm=Al.                              Mm 

=  Cr. 

Mra  =  Pe. 

Mol.  vol.     Solubility.          Mol.  vol. 

Solubility. 

Mol.  vol.    Solubility. 

M1  —  ~K 

546.9     0.28          550.8 

0.441 

JL\. 

NH4 

555.9     0.387        557.6 

0.407 

562.8      1.659 

Tl 

566.6     0.177        557.7 

0.234 

560.2     0.799 

Eb 

562.2     0.059        561.7 

0.079 

573.3     0.376 

Cs 

579.2     0.013        581.8 

0.015 

579.3     0.045 

M1  =  Cs. 

M'  = 

(NH4). 

Mol.  vol.      Solubility. 

Mol.  vol. 

Solubility. 

Mm  = 

Al        578        0.013 

555.9 

0.387 

Cr        582        0.015 

557.6 

0.407 

Fe        579        0.045 

562.8 

1.659 

In         584        0.172 

... 

.  .  • 

The  coincidence,  while  not  absolute,  shows  that  there  is  a 
close  connection  between  the  molecular  volumes  of  the  alums 
and  their  solubility.  The  variations,  furthermore,  lose  much  in 
weight  in  the  fact  that  a  very  small  error  in  the  determination 
of  the  specific  gravity  is  greatly  multiplied  in  the  quotient 

molecular  weight 
specific  gravity 

Solubility  at  Different  Temperatures.  —  The  next  question 
to  be  decided  was  whether  there  is  any  regularity  in  the 
effect  of  increasing  temperature  upon  the  solubility  of  dif- 
ferent alums.  Here  I  was  much  limited  in  my  choice  of  salts, 
insomuch  as  the  ferric  compounds  break  down  into  basic 
salts  when  treated  with  pure  water  at  higher  temperatures, 

*  Soret,  Arch.  sc.  phys.  nat.  Geneve,  xii,  563,  etc.  Arzruni,  Physikalische 
Chemie  der  Krystalle  (1893),  p.  130.  Soret's  original  article  is  not  at  my 
disposal. 


AND  INORGANIC  COMPOUNDS. 


185 


10 


30° 


Temperature 

FIGURE  HI. 


40° 


186 


THE  PERIODIC  SYSTEM 


and  the  chromic  compounds  pass  into  their  green  modifi- 
cations at  about  50°.  This  behavior  of  the  ferric  alums  pre- 
vented the  comparative  study  of  any  but  the  rubidium  and 
caesium  compounds.  As  I  wished  merely  to  find  the  general 
direction  of  the  solubility  curves,  I  did  not  carry  out  deter- 
minations at  temperatures  below  25°.  Experiments  on 
chromic  salts  showed  that  even  at  45°  they  became  slightly 
green  on  prolonged  digestion,  and  40°  was  therefore  taken  as 
the  upper  limit.  The  following  table  gives  the  solubilities  of 
the  rubidium  and  caesium  alums  of  aluminium,  chromium,  and 
iron,  at  intervals  of  5°  between  these  limits. 


Eb—  Al. 

Bb—  Or. 

Eb—  Pe. 

25° 

Pts.  per 
liter. 

18.1 

Gr.  mol. 
per  liter. 

0.059 

Pts.  per 
liter. 

25.7 

Or.  mol. 
per  liter. 

0.078 

Pts.  per 

liter. 

125.4 

Gr.  mol. 
per  liter. 

0.294 

30° 

21.9 

0.072 

31.7 

0.096 

202.4 

0.617 

35° 

26.6 

0.087 

41.1 

0.128 

Basic  salt 

separated. 

40< 


25° 

30° 
35° 
40° 


32.2      0.106          59.7      0.181 


Cs-Al. 

4.70  0.0130 

5.89  0.0167 

7.29  0.0207 

9.00  0.0256 


Cs— Cr. 

5.70  0.0150 

9.60  0.0250 

12.06  0.0320 

15.30  0.0405 


Cs-Pe. 

17.1  0.045 

25.2  0.066 
37.5  0.099 
60.4  0.156 


Fig.  Ill  shows  the  curves  corresponding  to  the  solubilities 
of  these  salts,  expressed  in  gram-molecules  per  liter.  To 
facilitate  comparison  the  solubilities  curves  of  the  rubidium 
salts  are  dotted. 

There  seems  here  to  be  no  marked  connection  between  the 
various  alums  with  respect  to  the  univalent  metals ;  the  curve 
of  CsFe(SO4)2  crossing  that  of  RbAl(SO4)2  at  about  33°. 
But  if  we  compare  the  alums  first  of  caesium  and  then  of 
rubidium,  we  see  that  the  more  soluble  the  alum  of  a  given 
univalent  metal  is  at  25°,  the  more  rapidly  does  its  solubility 
increase  with  the  temperature.  This  is  marked  even  in  the 
case  of  the  caesium  salts  of  aluminium  and  chromium,  the 


AND  INORGANIC  COMPOUNDS.  187 

solubilities  of  which  at  25°  are  almost  the  same  (0.013  and 
0.015  gr.  mol.)  The  curve  of  RbFe(SO4)2  could  be  followed 
only  to  30°,  as  at  35°  a  sparingly  soluble  basic  salt  separated 
from  the  solution;  and  the  extreme  difference  in  solubility 
shown  for  the  interval  25°-30°,  may  in  part  be  ascribed  to  a 
hydrolytic  action. 

Melting-points.  —  The  melting-point  of  a  hydrated  salt  is  of 
course  intimately  connected  with  its  solubility;  so  that  in 
studying  them  one  would  expect  results  approximately  anal- 
ogous to  the  above.  But  at  the  same  time  I  was  enabled  hi 
this  way  to  examine  a  greater  variety  of  alums,  including 
those  of  cobalt,  the  solubility  of  which  could  not  be  deter- 
mined, the  rubidium  indium  salt,  and  the  potassium-vanadium 
and  potassium-ferric  compounds. 

The  cobaltic  salts  examined  were  those  containing  rubidium 
and  caesium.  These  were  made  in  the  same  way  as  Marshall  * 
obtained  the  ammonium  and  potassium  cobaltic  alums,  by  the 
electrolytic  oxidation  of  cobaltous  sulphate  and  addition  of 
the  calculated  amount  of  the  salt  of  the  desired  alkali  metal. 
Both  compounds  came  down  in  coarse  crystalline  grains,  which 
could  be  readily  washed  by  lixiviation  with  cold  water.  They 
were  sufficiently  stable  to  permit  of  rapid  drying  in  the  air, 
but  on  standing  for  any  length  of  time  they  lost  oxygen  and 
yielded  cobaltous  sulphate.  The  rubidium  alum  decomposed 
in  this  matter  even  in  a  sealed  specimen  tube,  on  standing  for 
a  few  months.  The  caesium  compound,  however,  when  pre- 
served in  the  same  way,  has  still  retained  its  green  color ; 
thus  forming  an  interesting  example  of  the  greater  stability 
of  caesium  double  salts  over  those  of  rubidium.  Both  com- 
pounds crystallized  in  glistening  microscopic  octahedrons.  In 
view  of  their  marked  physical  properties,  it  was  not  deemed 
necessary  to  submit  them  to  a  full  analysis,  but  as  a  matter  of 
general  precaution  a  weighed  quantity  of  each  was  ignited  be- 
low a  red  heat,  and  the  amount  of  the  residual  cobaltous  and 
alkali-sulphates  determined. 

*  Soc.  Edinburgh,  lix,  760. 


188  THE  PERIODIC  SYSTEM 

0.0683  g.  RbCo(S04)2.12H20  gave  0.0361  g.  Rb2S04  +  CoS04 

calculated  0.0357  g. 

0.7004  g.  CsCo(S04)2.12H20  gave  0.2962  g.  Cs2S04  +  CoS04 

calculated  0.2959  g. 

The  determination  of  the  melting-points  was  carried  out  in 
sealed  capillary  tubes,  of  various  diameters,  and  about  two 
inches  in  length.  The  tubes  were  in  each  case  filled  to  some- 
what over  half  their  height  with  the  powdered  salts.  At  least 
five  determinations  were  made  on  each  compound,  and  samples 
from  several  different  preparations  used  for  each.  Variations 
in  the  manner  of  heating,  etc.,  introduce  comparatively  large 
errors  in  the  melting-points,  which  are  in  no  case  very  sharp. 
But  after  some  practice,  I  was  able,  by  carefully  following  one 
method  of  procedure,  to  reduce  the  error  to  about  1°  ;  and  in 
cases  where  two  alums  melted  at  about  the  same  point,  as  the 
NH4A1  (95°)  and  NH4Cr  (94°)  salts,  comparative  determina- 
tions were  made  side  by  side  in  the  same  apparatus.  So  while 
no  pretence  to  great  accuracy  in  these  determinations  is  made, 
the  errors  involved  are  at  least  about  the  same  for  each  com- 
pound, and  thus  the  data  given  below  are  not  vitiated  for  the 
purpose  of  comparison. 

The  literature  contains  various  notices  on  the  melting-points 
of  aluminium-  and  chromium  alums,  and  Piccini  also  deter- 
mined approximately  those  of  the  vanadium  salts  with  sodium 
(9°),  potassium  (20°),  and  ammonium  (50°).  The  last  I  find 
to  melt  at  45°,  and  for  vanadium  potassium  alum  I  have  ob- 
tained data  anywhere  from  20°  to  28°.  The  purification  of 
this  compound  is  so  difficult  that  a  constant  melting-point 
cannot  be  observed.  My  results  on  the  aluminium  alums  cor- 
respond fairly  well  with  those  of  Erdmann,*  though  being 
slightly  higher ;  and  both  his  and  mine  are  much  higher  than 
those  determined  by  Tilden.f 


Tilden   .    . 

Na—  Al  ; 

.     61 

K—  Al; 

84.5° 

NH4—  Al  ; 
92° 

Rb—  Al  ; 
99° 

Cs—  Al. 

106° 

Erdmann    . 

.     .  . 

92.5° 

. 

105° 

120.5° 

Locke    .    . 

.    63 

91° 

95° 

109° 

122° 

*  An.  Pharm.,  ccxxxii,  3.  f  London  Soc.  Trans.,  xlv,  266. 


125° 
120° 
115° 

105° 


Al) 


Al 


Al 


75° 


05° 


55° 


45° 


35° 


Atomic  "Weights, 


AND  INORGANIC  COMPOUNDS.  189 

Observations  on  sodium-chromium  and  csesium-indium  alums 
gave  no  satisfactory  results ;  the  fusion  process  in  each  case 
covering  a  range  of  about  ten  degrees,  and  in  the  case  of  the 
indium  salt,  being  even  then  imperfect.  My  complete  results 
follow : 

Mm  =  Al.  V.  Cr.  Fe.  Co.  In. 

M1  =  Na  63°  (9°)*  

K  91°  (20°)*        89°      28°       

Tl  91°  48°           92°      37°        

NH4  95°  45°            94°      40°        .  .       (36°)f 

Rb  109°  64°  107°      53°      47°        42° 

Cs  122°  82°  116°      71°      63° 

The  order  in  which  the  trivalent  metals  fall,  according  to 
the  melting  points  of  their  alums  with  a  given  univalent  metal, 
is  here  the  same  as  when  determined  by  the  solubility  relations 
of  their  salts.  The  one  exception  lies  in  the  doubtful  melting 
point  of  vanadium  potassium  alum,  which  is  a  few  degrees 
lower  than  that  of  the  corresponding  ferric  salt.  The  cobalt 
alums  melt  at  a  slightly  lower  .temperature  than  do  the  iron 
compounds,  and  indium  rubidium  alum  lower  than  any  other 
of  the  rubidium  salts,  just  as  the  indium  csesium  alum  is  the 
most  soluble  member  of  the  caesium  series. 

With  reference  to  the  univalent  metals  also,  the  same  grad- 
uation obtains  as  in  the  solubilities,  but  only  in  so  far  as  the 
alkali  metals  are  concerned.  The  order  of  the  thallium  and 
ammonium  series  is  changed,  the  thallium  salts  lying  next 
those  of  potassium.  The  vanadium  compounds  here  form  the 
only  exception,  and  in  view  of  their  great  instability  it  is  to  be 
doubted  whether  this  is  not  due  to  unavoidable  impurities. 

In  Figure  IV,  I  give  the  melting-points  plotted  as  a  func- 
tion of  the  atomic  weights  of  the  trivalent  metals,  Rm. 

Here  again  we  see  a  sharp  break  in  the  case  of  the  chromic 
salts.  The  melting  points  of  the  csesium  and  rubidium  alums 
of  aluminium,  vanadium,  iron,  and  cobalt  are  represented  by 
nearly  parallel  straight  lines,  which  would  indicate  a  very 

*  Piccini,  1.  c.  t  J.  Prakt.  Chemie  (2),  vii,  14. 


190  THE  PERIODIC  SYSTEM 

simple  relation  between  them,  and  the  atomic  weights  of  these 
metals.  But  we  must  either  admit  that  the  values  of  the 
melting-points  are  not  dependable  upon  the  atomic  weights, 
or  that  the  chromic  alums  form  an  exception  to  a  law  of 
nature. 

III.    THE  SOLUBILITIES   OF   ALUMS  AS  A  FUNCTION  OF 
Two  VARIABLES.* 

In  my  second  paper  in  this  series  f  I  attempted  to  show  that 
a  definite  gradation  can  be  traced  in  the  solubility  of  the 
alums  of  aluminium,  vanadium,  chromium,  and  iron,  severally, 
with  ammonium,  thallium,  rubidium,  and  caesium.  When  the 
solubilities  at  25°  of  the  sixteen  compounds  considered,  ex- 
pressed in  gram-molecules  per  liter  of  water,  are  plotted  as  a 
function  of  the  atomic  weights  of  the  trivalent  metals,  a  fig- 
ure of  remarkable  regularity  is  obtained.  The  solubilities  of 
the  alums  of  aluminium,  vanadium,  and  iron,  with  any  given 
alkali  metal,  increase  with  the  atomic  weights  of  the  trivalent 
metals  ;  and  this  increase  becomes  the  more  pronounced  as  we 
pass  from  the  caesium  alums,  through  those  of  rubidium  and 
thallium,  to  the  ammonium  salts,  successively.  But  the  alums 
of  chromium,  which  stands  between  vanadium  and  iron  in  its 
atomic  weight,  are  much  less  soluble  than  those  of  either  of 
the  latter  metals.  The  sharp  break  in  the  curves,  caused 
by  this  behavior  of  the  chromium  salts,  indicates  that  al- 
though the  method  of  plotting  employed  illustrates  the  gen- 
eral gradation  of  the  solubilities,  the  latter  cannot  truly  be 
regarded  as  a  function  of  the  atomic  weights.  The  solubil- 
ities, as  determined,  are  as  follows  : 


Mm  =  Al. 

v. 

Cr. 

Fe. 

Cs       0.013 

0.0204 

0.0151 

0.045 

Rb      0.059 

0.177 

0.078 

0.293 

Tl       0.177 

0.573 

0.212 

0.799 

NH4    0.387 

1.210 

0.407 

1.659 

Amer.  Chem.  Jour.,  xxvi,  August,  1901.        |  See  the  preceding  article. 


AND  INORGANIC  COMPOUNDS. 


191 


Cs  Mra(S04), 

— —- ^— ^^^^— 

Atomic  "Weights, 

FIGURE  I. 


51  52 


Fig.  1  reproduces  these  relations.     For  the  sake  of  clear- 
ness,   the   values   are    slightly  increased  along   the  a>axis. 


192  THE  PERIODIC  SYSTEM 

The  lines  joining  the  vanadium  and  chromium  alums  of 
each  univalent  metal  should,  in  reality,  be  nearly  perpendic- 
ular to  the  z-axis. 

A  careful  examination  of  this  figure  gives  at  the  outset 
one  striking  result,  which,  if  it  is  also  to  be  observed  in 
solubility  charts  of  other  series  of  homologous  compounds, 
may  lead  to  a  great  advance  in  our  knowledge  of  the  rel- 
ative influence  of  analogous  elements  upon  their  compounds. 

The  lines  joining  the  solubility  points  of  the  successive  univ- 
alent metals  with  two  given  trivalent  metals,  have  approximately 
a  common  point  of  intersection.  Thus,  the  line  joining  the  sol- 
ubility points  of  the  caesium  alums  of  vanadium  and  alumin- 
ium, on  prolongation,  meets  that  of  the  thallium  alums  of 
the  same  metals,  in  the  point  x=  16.25,  y  =  0.11 ;  the  unit  on 
the  z-axis  being  the  atomic  unit,  that  on  the  ?/-axis  one-hun- 
dredth of  a  gram-molecule.  The  points  of  intersection  of  the 
remaining  corresponding  lines  vary  only  slightly  from  this, 
and  on  either  side  of  it.  The  intersection  points  of  all  the 
aluminium-vanadium  lines  with  one  another  follow : 

Cs— Rb.         Rb— TL  Cs— Tl.  NH4— Cs.         NH4— Rb.        NH4— Tl. 

x  =  18.1       16.30        16.25        16.00        15.70        15.10 
y=    1.1         0.11          0.11          1.17          0.15          0.12 

The  following  are  the  points  of  intersection  of  the  vana- 
dium-chromium lines: 

Rb-Cs.  Tl-Cs.          Tl— Rb.          NH4— Cs.       NH4— Rb.         NH4-T1. 

x  =  52.99        52.6        52.65        52.6        52.6          52.53 
y=    1.2  1.3          0.8  1.4          1.45          5.3 

In  both  of  these  series  the  nearest  approximation  of  the 
points  of  intersection  to  a  single  point  is  seen  to  be  in  the 
case  of  those  lines  which  intersect  at  the  greatest  angle. 
The  most  marked  variations  are  that  of  the  (AlCs— VCs)  and 
(AlRb— VRb)  lines  hi  the  first  series,  and  that  of  the 
(VTl-CrTl)  and  (VNH4-CrNH4)  lines  in  the  second;  that 
is,  where  the  lines  in  question  are  most  nearly  parallel,  and 
where,  therefore,  unavoidable  error  of  experiment  would  pro- 


AND  INORGANIC  COMPOUNDS. 


193 


duce  the  greatest  divergence.  The  various  other  lines,  such  as 
those  of  (FeM'-CrM1),  (FeM-AlM1),  or  (CrM'-AlM1), 
show  a  similar  relation  as  regards  their  points  of  intersec- 
tion, and  it  must  be  assumed,  therefore,  that  the  points  rep- 
resenting the  solubilities  stand  in  fixed  mathematical  relation  to 
one  another. 

This  being  so,  the  derivation  of  a  general  formula  for  the 
calculation  of  the  solubility  of  the  sixteen  alums  in  question 
is  a  comparatively  simple  matter.  The  first  step  involved  is 
the  empirical  determination  of  the  fixed  points,  of  which  the 
observed  points  of  intersection  are  approximations.  Of 
these,  the  three  giving  respectively  the  intersections  of  the 
lines  (VM'-AIM1),  (VM'-CrM1)  and  (CrM'-FeM1)  are 
required. 

The  points  finally  selected  as  most  nearly  satisfying  all  the 
solubilities  are  as  follows  : 


For  (VM'  -  AIM') 


Radii  drawn  from  these  points  gave  by  intersection  with 
perpendiculars  raised  on  the  #-axis  at  points  corresponding  to 
the  atomic  weights  of  the  trivalent  metals,  the  following  solu- 
bilities in  gram-molecules.  Under  D  is  given  the  variation 
from  the  observed  solubilities. 


M^Al 

D. 

V. 

D. 

Cr. 

J>. 

Fe. 

D. 

M'=Cs 
Rb 
Tl 

NH4 

0.012 
0.064 
0.182 
0.382 

-0.001 
+0.005 
4-0.005 
-0.006 

0.0209 
0.1878 
0.5670 
1.2090 

+0.0005 
+0.0108 
-0.0060 
-0.0010 

0.0169 
0.0734 
0.2014 
0.4182 

+0.0018 
-0.0046 
-0.0106 
+0.0112 

0.0498 
0.2776 
0.7922 
1.6643 

+0.0048 
-0.0169 
-0.0068 
+0.0016 

Average  enror, 

+0.001 

+0.001 

-0.0005 

-0.0043 

13 


194  THE  PERIODIC  SYSTEM 

As  is  seen,  the  agreement  between  the  observed  and  calcu- 
lated data  is  in  the  main  very  satisfactory.  In  more  than  half 
the  cases  the  difference  does  not  exceed  0.005  gram-molecule. 
The  average  molecular  weight  of  an  alum  is  about  300,  and 
the  error  represented  by  a  difference  of  0.001  gram-molecule 
therefore  means  about  0.3  g.  per  liter.  As  the  majority  of 
my  determinations  were  made  with  quantities  of  solutions 
containing  about  3.0  g.  of  water,  therefore,  an  error  of  this 
magnitude  would  represent  on  the  average  less  than  a  milli- 
gram in  weight ;  or  in  the  case  of  the  ammonium  alums,  where 
the  dissolved  salts  were  determined  as  sesquioxides,  less  than 
0.5  milligram.  A  very  slight  variation  in  temperature,  in  the 
case  of  the  more  soluble  alums,  introduces  a  still  greater  error. 
At  30°,  one  liter  of  water  dissolves  0.467  gram-molecule 
ammonium  aluminium  alum,  and  0.495  gram-molecule  ammo- 
nium chromium  alum.  The  increase  in  solubility  for  5°  is 
therefore  in  the  one  case  0.080,  in  the  other  0.088  gram-mole- 
cule. Assuming  that  for  so  short  an  interval  the  solubility 
is  directly  proportional  to  the  temperature,  a  variation  of 
0.2°  would  cause  an  error  of  more  than  0.003  gram-molecule. 
The  range  of  solubility  of  the  alums  is  so  great  that  errors  of 
such  magnitude  would  have  little  influence  upon  the  deter- 
mination of  the  general  solubility  relations  of  the  salts ;  and 
such  relations  were  all  that  I  had  hoped  to  establish  by  the 
work  embodied  in  my  last  paper.  If  we  take  into  account  the 
effect  which  the  more  or  less  extensive  hydrolytic  dissociation 
of  the  sulphates  of  the  trivalent  metals  would  have  upon  the 
solubility  of  the  alums,*  the  variation  between  the  solubilities, 
calculated  and  observed,  is  in  almost  every  case  well  within 
the  limit  of  permissible  error.  In  the  derivation  of  the  con- 
stants used  in  this  paper,  therefore,  the  calculated  results  will 
be  taken  as  correct. 

The  prolongation  of  the  aluminium-vanadium  lines  and  of 
the  vanadium-chromium  lines  to  their  respective  points  of 
intersection  yields  a  series  of  triangles  which  have  a  common 

*  This  of  course  also  applies  to  the  formation  of  small  quantities  of  basic 
salts  on  evaporation  of  the  solutions  for  analysis. 


AND  INORGANIC   COMPOUNDS. 


195 


base  in  the  line  connecting  these  points.  A  similar  set  of 
triangles  is  given  by  the  intersection  of  the  vanadium-chro- 
mium lines  with  those  of  chromium-iron.  The  resulting 
figure,  somewhat  distorted  in  its  proportions,  is  shown  in 
Fig.  II. 


The  perpendiculars,  AA1,  BV,  CCr,  and  DFe,  and  the 
fixed  points,  P,  Q,  and  S  being  given,  the  points  of  intersec- 
tion of  the  radii  from  P,  Q,  and  S  with  the  perpendiculars  B V, 
CCr,  and  DFe,  are  necessarily  determined  by  the  position  of 
the  points  of  intersection  of  the  corresponding  radii  from  P 
with  the  perpendicular  AA1.  Now  the  points  AI,  B!,  Ci,  and 
Dj  represent  the  solubilities  of  the  caesium  alums  of  the  suc- 
cessive trivalent  metals;  A2,  B2,  C2,  and  D2,  those  of  the 
rubidium  alums,  etc.  The  line  AiP  makes  a  definite  angle,  6, 


196  THE  PERIODIC  SYSTEM 

with  the  a>axis,  and  the  points  B1?  Ci,  DI,  are  accordingly 
determined  by  the  value  of  this  angle.  If  we  substitute  rubid- 
ium for  caesium,  6  receives  another  value  and  B,  C,  and  D 
become  B2,  C2,  D2.  The  effect  of  the  substitution  of  any  one 
alkali  metal  for  another  in  the  alums  of  a  trivalent  metal  is 
therefore  always  measurable,  directly  or  indirectly,  by  the 
difference  in  the  values  of  6  peculiar  to  the  alkali  metals  in 
question. 

The  absolute  values  of  the  angle  6  are  fixed  by  the  relative 
positions  of  the  perpendiculars  AA1  and  B V  upon  the  #-axis ; 
but  these  do  not  affect  its  relative  values;  for  if  AA1,  for 
instance,  be  moved  in  either  direction,  the  point  P  still  re- 
tains its  y  value,  and  therefore  the  relation 

tan  0!      APA2      AP'A'2 

— — T-  =  -: — 7—  =  -T — 7-7-  =  const. 

tan  0      ApAi      Ap>A  \ 

remains  the  same  in  all  cases.  0  is  accordingly  a  variable 
peculiar  to  the  alkali  metals  in  the  compounds,  and  independ- 
ent of  the  trivalent  metals.  The  same  is  true  of  the  variable 
distance  PA  (/>),  which  depends  directly  upon  the  value  of 
0,  in  the  sense, 

p  sin  0  =  AAP  =  const. 

for  each  of  the  alkali  metals,  and  without  regard  to  the  posi- 
tion of  the  perpendiculars. 

The  effect  of  the  trivalent  metals  upon  the  solubility  is 
also  given  by  a  variable  which  has  a  constant  value  for  each. 
As  intercepts  of  two  sides  of  a  triangle  by  parallel  lines,  the 
relations  obtain : 

.  A2B2  .    A3B8 
"  A2P       A8P  = 


C2Q 

"scT 


AND  INORGANIC  COMPOUNDS.  197 

These  constants,  k,  ki,  and  &2,  are  independent  of  the  value 
of  the  angle  0,  and  therefore  of  the  univalent  metals  in  the 
alums.  They  are  also  independent  of  the  positions  of  the 
perpendiculars  AA1,  etc.  If  the  relative  positions  of  AA1 
and  BV  be  altered,  for  instance,  until  P  becomes  P'  (Fig.  Ill), 

A  'B  ' 

the  ratio  between  the  new  intercepts,  A  *,   *  ,  is  still  the  same  as 

AT>  AI  r 

l-Dl  7 

or  *. 
We  have,  furthermore,  the  relation, 

_  _  PA  +  AB  _  P  (k  +  1)  _  ^  . 


A^  ~   A2A3  PA 

Similarly,  for  the  vanadium  and  chromium  alums, 
dd      C2C8  dQ  1 


BiB,,      B2B8      CiQ  +  kiCQ      kt  -f  1 
D^      D2D8  SO  + 


Now  AiA2  represents  the  difference  in  solubility  of  the 
aluminium  alums  of  rubidium  and  caesium ;  CiC2,  that  of  the 
chromium  alums,  etc.  If  we  call  the  difference  in  the  solu- 
bility of  the  alums  of  a  given  trivalent  metal  with  two  alkali 
metals  the  "  increment  of  solubility  for  the  latter "  (e.  g., 
Incr-Al^c,,),  we  arrive  at  the  general  law: 

The  ratio  between  the  increments  of  solubility  of  the  corre- 
sponding alums  of  two  trivalent  metals  for  any  two  alkali 
metals  is  constant. 

The  constant  k  indirectly  represents,  therefore,  the  effect 
of  the  substitution  of  vanadium  for  aluminium  in  the  alum 
of  a  given  univalent  metal;  A?lt  that  of  chromium  for  vana- 
dium, etc.  And  since  the  value  of  these  constants  is  not 
affected  by  the  relative  positions  of  the  perpendiculars  upon 
the  a>-axis,  the  atomic  weights  of  the  trivalent  metals  have 
no  determining  influence  upon  them.  The  solubilities  cannot, 
therefore,  be  regarded  as  a  function  of  these  atomic  weights. 


198  THE  PERIODIC  SYSTEM 

The  values  of  the  constants  k,  etc.,  for  the  calculated  solu- 
bilities are  as  follows  : 

k  =  2.2110 
A*  =  1.9608 
k2  =  3.0213 

By  substitution,  we  have,  furthermore,  for  the  ratio  be- 
tween the  solubility  increments  of  the  alums  of  other  pairs 
of  trivalent  metals, 

CiC2  _  Incr.Crm*_m'  _  k  +  1  _ 
~"  Incr.Alm2_m'      k±  +  1 


= 

^ 


Incr.Alm2_m/      k{  +  I 

_m/  _  k2  +  1  _ 

~  ~ 


Owing  to  the  large  error  introduced  into  the  quotient  of 
the  observed  solubility  increments  by  variations  of  a  few 
thousandths  of  a  gram-molecule  in  the  solubility  determina- 
tions, we  can  expect  only  an  approximate  agreement  between 
the  above  constants  and  their  observed  values.  The  latter, 
which,  together  with  the  variations  from  the  calculated  values 
(D),  are  given  below,  are  therefore  eminently  satisfactory. 
The  agreement  between  them  is  so  marked  that  there  can  be 
no  doubt  as  to  the  correctness  of  the  law. 

Incr.Alm2_m>  Incr.Om2_m, 

=  0.6611 


.  — 

Incr.  Vm2_m>  Incr.  V 


m».  m'.  Observed.  D.  Observed.                   D. 

NH4  Cs  3.181  -0.030  0.3295  -0.0085 

Tl  Cs  3.378  +0.167  0.3561  +0.0184 

Eb  Cs  3.404  +0.190  0.4016  +0.0693 

NH4  Kb  3.149  -0.074  0.3185  -0.0192 

Tl  Eb  3.356  +0.145  0.3384  +0.0007 

NH4  Tl  3.033  —0.178  0.3197  —0.0316 


AND  INORGANIC   COMPOUNDS. 


199 


Incr.Fe 


Incr.Crm2_m' 


=  4.021 


Incr.Or 


Incr.Al 


m2— m' 


m*. 

m'. 

Observed. 

D. 

NH4 

Cs 

4.118 

+0.097 

Tl 

Cs 

3.829 

-0.192 

Kb 

Cs 

3.957 

-0.064 

NH4 

Kb 

4.119 

+0.098 

Tl 

Kb 

3.770 

-0.250 

NH4 

Tl 

4.410 

+0.389 

Observed. 

1.021 
1.200 
1.152 
1.003 
1.127 
0.927 


=  1.084 


D. 

-0.063 
+0.116 
+0.068 
-0.081 
+0.043 
-0.159 


Incr.Fem2_m' 
Incr.Alm2_m/ 


=  4.360 


Incr.Fe 


m8 — m' 


m2. 

m'. 

Observed. 

D. 

NH4 

Cs 

4.316 

-0.044 

Tl 

Cs 

4.537 

+0.177 

Kb 

Cs 

5.411 

+1.051 

NH4 

Kb 

4.164 

-0.196 

Tl 

Kb 

4.200 

-0.080 

NH4 

Tl 

4.095 

-0.265 

Incr.Vm2_m/ 

Observed. 

1.357 
1.363 
1.606 
1.322 
1.276 
1.350 


=  1.358 


D. 

-0.001 
+0.005 
+0.186 
-0.031 
-0.067 
-0.008 


The  only  marked  deviations  from  the  calculated  constants 

,    ,,     . 
where  both  increments  are 


£  Incr.CrRb_c_ 
are  in  the  case  of 


Tr 
Incr.VEb_c8 

so  small  that  even  the  slightest  error  of  experiment  has  a 
great  influence  upon  their  ratio  ;  and  in  some  of  the  ratios 
obtained  with  rubidium  ferric  alum.  The  observed  solubility 
of  this  salt  is  probably  somewhat  high,  owing  to  the  readiness 
with  which  it  undergoes  hydrolysis.  The  error  thus  intro- 
duced, however,  becomes  very  great  only  in  the  ratios 

Incr.FeRb_C8 


In  the  ratios 


Incr.M 


its  influence  is 


Incr.M  Rb_C8 
hardly  felt. 

The  remaining  variables  of  the  triangles  PBQ  and  SCQ, 
so  far  as  their  values  are  necessary  for  the  derivation  of  a 
general  formula  for  the  solubilities,  are  also  to  be  expressed 
in  terms  of  0,  and  &,  kl9  etc. 


200  THE  PERIODIC  SYSTEM 

If  we  call  the  angle  of  inclination  of  the  base  line  PQ  to 
the  2>axis,  a,  then  for  the  variable  angle,  BQP,  or  fa  we 
have  the  expression  : 

PB  sin  (Q  -  a)  P(£+l)sm(0-q) 

Q  *  ~~  PQ  -  PB  cos  (0  —  a)  ~~  PQ  -  P  (k  +  1)  cos  (0  -  a)  " 

In  this  formula,  a  and  PQ  are  constant.     Substituting  for 
the  latter  and  k  their  calculated  values,  we  have, 

_         p  sin  (0  —  q)         __  ~ 
Q  *~  11.37  -p  cos  (0-a)  = 

_  n      BiP  sin  (0  -  a) 

Since  BiQ  =  -          -A-  -  *-> 

Bin  9 

the  variable  distance  BQ  becomes 


p(A  +  1)  sin  (0  -  a)  VTT^5       ,.. 
-5- 

As  the  intercepts  BC  =  ki  CQ  and,  therefore, 
M  =  BC  +  ^, 

KI 

the  relation  which  these  intercepts  bear  to  M  are 

BC  =  A^j-  and  CQ  =  r^T- 
*i  +  1  *!  +  1 

The  base  line  SQ  makes  with  the  a>axis  the  constant 
angle  @  ;  the  variable  angle  BQS  is  therefore  </>  +  ft  —  a. 
For  the  angle  DSQ,  or  2,  we  have,  as  in  the  case  of  the 
angle  <£, 

tanS-        CQ  sin  (<£  +  /?  -  a) 

"  SQ  -  CQ  cos  (<j>  +  ft  -  a)  ' 

The  value  of  a  is  1°  5'  54",  and  that  of  A  26°  33'  54".    Ex- 


AND  INORGANIC  COMPOUNDS.  201 

panding,  and  substituting  for  these  and  SQ  their  correspond- 
ing values,  and  for  CQ  its  equivalent,  —    -  =  » 

KI  -f-  i.      >s.youo 

we  have 

Jf(#  +  0.4763) 

~"  6.401  VI  +  IP  —  M  (1  -  0.4763  J?)  * 

The  distance  AAP  =  p  sin  0.     The  solubility  of  the  aluminium 
alums  is  therefore  expressed  by  the  equation, 

S^  =  m  +  p  sin  0  (I) 

m  being  the  y-value  of  the  point  P.     For  the  solubility  of  the 
vanadium  alums  we  have, 


BBP  =  BBA  +  AAW  (2) 

and  since  BBA  =  k  p  sin  0, 

by  addition  with  (1), 

Sv  =  m  +  p  sin  0  +  k  p  sin  0. 

Passing  in  the  same  manner  to  the  chromium  alums, 
CCP  =  BBP  -  BBC 

=  BB,-A£1  sin  (*-«), 
and,  accordingly, 

Sc,  =  m  +  p  sin  0  +  k  p  sin  0  —  ,  l    1  sin  (<#>  —  a).         (3) 

k\  ~r  J- 

The  points  D1?  D2»  e^c.,  are  expressed  by 
SFe  =  m  +  DDP 

=  m  +  DD0  +  CCP 

in  which  DDC  =  CD  sin  (2  +  /3). 

The  variable  distance  CD  is  given  by  the  equation, 


CQ  sin  (<ft  +  /?  —  a) 

sin  2 


202  THE  PERIODIC  SYSTEM 

ft  +  /?  —  a) 


(&!  +  1)  sin  S 
Substituting  this  value  for  CD,  we  have 


or 

k  M 
S^  =  m  +  p  sin  0  +  k  p  sin  0  —  ^  —  T  sin  (<£  —  a)  + 

»1  T*  1 


This  also  serves  as  a  general  formula  for  the  solubility  (S) 
of  any  of  the  sixteen  alums  taken  into  consideration.  For  if 
k2  be  made  equal  to  zero,  the  last  term  falls  away,  leaving  the 
equation  in  the  forms  applying  to  the  chromium  alums.  With 
kz  and  k^  equal  to  zero,  the  solubilities  of  the  vanadium  alums 
are  obtained,  and  by  eliminating  the  second  term  as  well, 
those  of  the  aluminium  salts.  We  thus  have  a  general  solu- 
bility equation,  all  the  terms  of  which  can  be  referred  to  two 
variables;  the  one  of  these,  0,  applying  to  the  one  class  of 
elements  in  the  compounds,  the  other,  &,  to  the  second  class. 
I  believe  that  aside  from  the  instance  of  addition  properties, 
which  the  solubilities  certainly  are  not,  this  is  the  first  case 
in  which  a  mathematical  relation  between  the  corresponding 
properties  of  a  class  of  compounds  has  been  found  capable  of 
expression. 

Below  I  give  the  values  of  6  and  p  for  each  of  the  alkali 
metals,  and  the  solubilities  as  calculated  by  the  general 
formula.  With  the  latter,  the  column  D  contains  the  dif- 
ference between  the  calculated  and  observed  solubilities,  and 
D'  the  variation  from  the  values  serving  as  a  basis  for  the 
derivation  of  the  constants. 

9  p 

Cs     .     .    .    .      2°    6'    6"  10.945 

Eb    ....    27°  11'  19"  12.254 

Tl     ....     57°  56'    4»  20.5406 

73°  45'    5"  38.943 


AND  INORGANIC  COMPOUNDS. 


203 


In  the  following  the  solubilities  are  expressed  in  hundredths 
of  a  gram-molecule : 


Al. 

D. 

D'. 

J 
II 

M 

D. 

D'. 

o- 
II 

J4 

D. 

D'. 

w 

*« 

Jf 

D. 

D'. 

Cs 
Rb 
Tl 
NH4 

1.192 
6.38 
18.21 
38.18 

-0.0108 
+0.328 
+0.510 
+0.520 

-0.008 
-0.020 
+0.010 
-0.020 

2.06 
18.90 
56.7 
120.82 

+0.02 
+1.20 
-0.60 
-0.08 

-0.03 
+0.12 
0.00 
-0.07 

1.671 
7.34 
20.13 
41.82 

+0.16 
-0.36 
-1.07 
+1.12 

-0.02 
0.00 
+0.01 
0.00 

4.82 
27.76 
79.69 
165.26 

+0.32 
-1.63 
-0.30 
-0.64 

-0.16 
+0.06 
+0.47 
-1.17 

In  conclusion  I  may  state  that  while  the  data  now  at  hand 
are  too  few  for  accurate  analysis,  such  determinations  as  I 
have  made  at  temperatures  other  than  25°  indicate  that  a 
general  solubility  formula  for  all  temperatures  will  not  be 
difficult  of  derivation.  I  have  made  determinations  at  30°  on 
the  caesium,  rubidium,  and  ammonium  alums  of  aluminium, 
chromium,  and  iron ;  and  find  that  the  law  of  the  constant 
ratio  of  the  solubility  increments  holds  good  at  that  tempera- 
ture. The  value  of  the  constants  &,  k^  and  &2>  however,  vary 
with  the  temperature.  At  30° 


Incr.Crm2_m' 
Incr.Alm2_m/ 


=  1.20,  and 


Incr.Fema-m 
Incr.Crma_mi 


=  8.3 


in  approximate  numbers.  From  the  fact  that  this  law  obtains 
at  other  temperatures,  it  necessarily  follows  that  at  these,  as 
at  25°,  the  lines  joining  the  solubility  points  have  common 
points  of  intersection.  The  same  formula,  therefore,  with 
other  constants,  obtains  at  different  temperatures.  The 
mathematical  relation  between  the  solubilities  at  25°  cannot, 
accordingly,  be  a  matter  of  chance. 

My  thanks  are  due  to  Eugene  Lamb  Richards,  Professor  of 
Mathematics  in  Yale  University,  for  many  helpful  suggestions 
embodied  in  this  paper. 


PAPERS  ON 
DOUBLE  HALOGEN  SALTS 


ON  SOME  DOUBLE  HALIDES  OF  SILVER  AND 
THE   ALKALI  METALS.* 

BY  H.  L.  WELLS  AND  H.  L.  WHEELER. 

WITH   THEIR  CRYSTALLOGRAPHY. 

BY  S.  L.  PENEIELD. 

DURING  a  systematic  search  for  well-crystallized  salts  of  the 
type  M'Hl.AgHl,  f  which  we  were  anxious  to  obtain  on  ac- 
count of  their  probable  isomorphism  with  the  alkaline  tri- 
halides,  three  well-defined  compounds  of  another  type, 
2M/Hl.AgHl,  were  obtained.  Our  experience  indicates  that 
these  2  :  1  salts  are  more  easily  prepared  and  crystallize  better 
than  the  1  :  1  compounds. 

The  bodies  to  be  described  are  2CsCl.AgCl,  2RbI.AgI,  and 
2KI.AgI.  Two  of  these  are  believed  to  be  new  salts;  the 
other,  2KI.AgI  has  been  described  by  Boullay.J  We  have 
not  obtained  a  complete  series  of  these  compounds,  for  good 
crystals  could  not  be  made  of  the  other  members,  and,  under 
the  circumstances,  no  products  were  analyzed  except  such  as 
could  be  measured. 

The  compounds  are  interesting  from  the  fact  that  they  do 
not  conform  to  Remsen's  law  concerning  the  composition  of 
double  halides,  §  for,  contrary  to  this,  they  contain  a  number 
of  alkali-metal  atoms  which  is  greater  than  the  number  of 
halogen  atoms  belonging  to  the  silver.  In  his  latest  contribu- 
tion to  the  subject,  ||  Remsen  states  that  the  exceptions  to  his 
law  are  "not  more  than  three  or  four  out  of  over  four 

*  Amer.  Jour.  Sci.,  xliv,  August,  1892.         §  Amer.  Chem.  Jour.,  xi,  291. 
t  Ibid.,  Ill,  xliii,  30  and  485.  ||  Ibid.,  xiy,  87. 

J  Ann.  Chim.  Phys.,  II,  xxiv,  377. 


208  SOME  DOUBLE  HALIDES   OF  SILVER 

hundred."  The  work  here  described  confirms  the  result  of 
Boullay,  adds  two  more  exceptions  to  the  law,  and  points  to 
the  existence  of  a  greater  number  of  compounds  of  the  same 
type.  It  may  be  mentioned  that  a  considerable  number  of 
other  exceptions  to  this  law  have  recently  been  established  in 
this  laboratory  and  will  soon  be  described. 

Preparation  and  Properties.  —  The  salts  are  made  by  satu- 
rating a  very  concentrated,  hot  solution  of  an  alkaline  halide 
with  the  corresponding  silver  halide,  filtering,  cooling  to 
crystallization,  and,  if  necessary,  evaporating  the  mother-liquor 
at  ordinary  temperatures.  If  the  solutions  are  too  dilute,  in 
some  cases  at  least,  the  1  :  1  salts  are  formed.  The  com- 
pounds have  little  tendency  to  crystallize  well,  and  many  trials 
are  usually  necessary  in  order  to  obtain  satisfactory  products. 
The  salts  are  all  white.  They  are  readily  decomposed  by 
water. 

Method  of  Analysis.  —  The  products  analyzed  were  in  the 
form  of  crystals  of  such  size  that  it  was  certain  that  they  were 
not  mixed  with  other  substances.  In  preparing  them  for 
analysis  the  mother-liquor  was  removed  rapidly  and  completely 
by  pressing  them  between  smooth  filter-papers,  and  great  care 
was  taken  to  avoid  any  evaporation  of  the  liquid  which  ad- 
hered to  them.  The  analyses  were  made  by  treating  them 
with  a  sufficient  amount  of  water  acidified  with  nitric  acid 
and  weighing  the  silver  halide  thus  separated.  The  filtrate 
from  this  was  used  for  determining  the  remaining  halogen  or 
the  alkali  metal. 

TfnnnA  Calculated  for 

2CsCl.AgCl. 

Caesium 55.38 

Silver 24.85  22.47 

Chlorine 22.15 

iPniin<i  Calculated  for 

Found.  2RbI.AgI. 

Bubidium     .     .    .    25.05  25.91 

Silver 17.32  16.36 

Iodine      ....    57.53  57.73 

99.90  100.00 


AND  THE  ALKALI  METALS. 


209 


Found. 

Potassium 

Silver 18.73 

Iodine 


Calculated  for 
2KI.AgI. 

13.79 
19.04 
67.17 


Crystallography. 

The  three  salts  are  isomorphous  and  crystallize  in  the  ortho- 
rhombic  system.     The  forms  which  were  observed  are : 


a,  100,  i-i 

b,  010,  i-i 


m,  110,  I 
n,   120,  i-2 


d,  101,  1-t 
x,  301,  3-£ 


The  axial  ratios  and  some  of  the  prominent  angles  are  given 
in  the  following  tables,  the  fundamental  measurements  being 
marked  by  an  asterisk.  The  crystals  did  not  yield  very  accu- 
rate measurements. 

U  :  ~b      :      c 

0.244 
0.236 
0.234 

d  A  d,  101  A  foi 

*28'  11' 
*27'  12' 
*27'  0' 


2CsCl.AgCl.  .  .  . 
2EbI.AgI  .  .  .  . 
2KI.AgI  .  .  .  . 

m  A  m,  110  A  110 

2CsCl.AgCl  .  .  88°  18' 
2EbI.AgI  .  .  .  *88°  40' 
2KI.AgI  .  .  .  *88°  40' 


0.971  :  1 
0.977  :  1 
0.977  :  1 

n  A  n,  120  Al20 

*54°  29' 
54°  12' 
54°  12' 


V 

771 

d 

a 

*~*^ 
m 

^ 

n 

Fig.  1. 


Fig.  2. 


2CsCl.AgCl  was  made  in  minute  prisms,  less  than  a  milli- 
meter in  diameter,  having  the  habit  shown  in  Fig.  1.  The 
measurements  are  only  approximately  correct. 

14 


210  HALIDES  OF  SILVER  AND   THE  ALKALI  METALS. 

Two  crops  of  2RbI. Agl  were  examined.  One  was  like  Fig.  1 
in  habit,  the  other  in  plates,  Fig.  2.  The  crystals  were  nearly 
10  mm.  in  length.  On  this  salt  a  cleavage,  parallel  to  a,  was 
observed;  also,  as  small  faces,  the  forms  b  and  x,  which  are 
not  shown  in  the  figures.  In  convergent  polarized  light  an 
obtuse  bisectrix  was  seen,  normal  to  a,  the  axial  plane  being 
the  brachy-pinacoid. 

2KI.AgI  was  made  in  prismatic  crystals,  over  10  mm.  in 
length  and  having  the  habit  and  forms  shown  in  Fig.  1. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
April,  1892. 


ON  THE   CAESIUM  AND  RUBIDIUM  CHLOR- 
AURATES  AND  BROMAURATES.* 

BY  H.  L.  WELLS  AND  H.  L.  WHEELER. 
WITH  THEIR  CRYSTALLOGRAPHY. 
BY  S.  L.  PENFIELD. 

A  STUDY  of  the  compounds  to  be  described  was  undertaken 
in  the  hope  that  some  crystallographic  analogy  would  exist  be- 
tween them  and  the  alkaline  pentahalides  described  in  a  pre- 
vious article. f  No  such  analogy  has  been  found  in  spite  of 
the  similarity  of  such  formulae  as  CsCl.Cl8I  and  CsCl.Cl3Au, 
but  since  some  of  these  gold  salts  have  never  been  described 
and  as  they  show  some  interesting  relations  among  themselves, 
our  results  are  deemed  worthy  of  publication.  J 

Th.  Rosenbladt,§  in  an  article  on  the  solubility  of  the  chlor- 
aurates,  states  that  the  caesium  and  rubidium  salts  lose  their 
water  of  crystallization  almost  completely  when  dried  over  sul- 
phuric acid.  He  gives  no  statement  of  the  amount  of  water, 
but  refers  to  his  dissertation  of  1872,  which  is  inaccessible  to 
us.  He  mentions,  however,  that  the  crystals  of  both  salts  be- 
long to  the  monoclinic  system,  so  that  it  is  probable  that  the 
compounds  he  obtained  were  the  ones  that  we  have  found  to  be 
anhydrous. 

The  compounds  that  have  been  prepared  are  CsAuCl4, 
2CsAuCl4.H2O,  CsAuBr4,  RbAuCL.,  and  RbAuBr*.  We 
have  attempted  in  each  case  to  obtain  bodies  containing  more 

*  Amer.  Jour.  Sci.,  xliv,  August,  1892. 

t  Ibid.,  42. 

J  The  announcement  by  Professor  Eemsen  (Amer.  Chem.  Jour.,  xiv,  89), 
that  he  and  Mr.  H.  C.  Jones  proposed  to  examine  the  gold-rubidium  halides, 
was  not  made  until  after  the  work  described  in  this  article  had  been 
completed. 

§  Berichte,  xix,  2535. 


212  ON  THE   CESIUM  AND  RUBIDIUM 

caesium  and  rubidium,  but  no  evidence  of  their  existence  has 
been  found. 

An  investigation  of  the  corresponding  iodine  compounds 
was  also  undertaken,  but,  on  account  of  the  instability  of 
auric  iodide,  we  did  not  obtain  any  pure  or  well-crystallized 
products. 

Preparation.  —  The  salts  are  so  insoluble  that  they  form 
precipitates  when  moderately  concentrated  solutions  of  the 
component  salts  are  mixed,  and  the  products  are  readily  re- 
crystallized  from  water  or  from  the  mother-liquors.  It  is 
usually  immaterial  whether  the  solutions  are  neutral  or  acid 
or  whether  the  gold  or  alkaline  halide  is  in  excess,  but  the  salt 
2CsAuCl4.H2O  requires  special  conditions  for  its  preparation, 
for  it  is  apparently  formed  only  when  a  large  excess  of  gold 
chloride  is  present  and  when  the  solution  does  not  contain 
much  free  acid.  We  have  used  four  atoms  of  gold  to  one  of 
csesium  in  making  this  salt,  but  it  usually  requires  repeated  tri- 
als under  these  conditions  before  it  is  obtained  free  from  the 
anhydrous  compound.  The  two  salts  are  however  so  distinct 
in  form  that  there  is  no  difficulty  in  distinguishing  them. 

Properties.  — The  color  of  CsAuCl4  and  of  2CsAuCl4.H2O 
is  golden-yellow ;  RbAuCl4  is  yellowish-red ;  the  two  bromides 
are  black,  but  give  a  dark  red  powder. 

All  the  salts  are  sparingly  soluble  in  water,  especially  when 
cold,  and  the  csesium  compounds  are  less  soluble  than  the  ru- 
bidium. All  of  them  are  only  slightly  soluble  in  alcohol  and 
insoluble  in  ether. 

Methods  of  Analysis.  —  The  crystals  were  prepared  for  anal- 
ysis by  quickly  pressing  them  between  smooth  filter-papers 
and  finally  allowing  them  to  become  air-dry.  The  hydrous 
caesium  chloraurate,  however,  loses  its  water  and  becomes 
opaque  on  exposure.  It  was  therefore  dried  as  rapidly  and 
thoroughly  as  possible  on  paper,  and  was  put  into  a  weighing- 
tube  as  soon  as  some  of  the  fragments  began  to  lose  their 
transparency. 

Gold  was  determined  by  precipitation  with  ammonium  oxa- 
late  or  with  sulphurous  acid.  The  filtrate  from  the  metallic 


CHLORAURATES  AND  BROMAURATES. 


213 


gold  was  used  either  to  determine  the  alkali  metal  as  normal 
sulphate  or  the  halogen  by  the  usual  gravimetric  method. 
Water  was  determined  by  the  method  used  in  the  combustion 
of  organic  compounds,  the  halogens  being  held  back  by  a  mix- 
ture of  lead  chromate  and  lead  oxide.  The  absence  of  water 
in  the  anhydrous  compounds  was  established  by  the  use  of  the 
same  process. 


Caesium 
Gold  . 
Chlorine 


Caesium 
Gold  . 
Chlorine 
Water 


Caesium 

Gold 

Bromine 


Rubidium 
Gold  .  . 
Chlorine 


Rubidium 
Gold  .  . 
Bromine 


Pound. 


27.23 
40.23 
29.07 
2.32 
98.86 


2.37< 


2.20* 


Found. 

20.73       .  .  . 
30.32      30.26 
49.31 


100.36 

FouncL 

45.53 
32.98 

Found. 

32.54 


Calculated  for 
CsAuCV 

28.16 
41.77 
30.06 


Calculated  for 
2CsAuCl4.H2O. 

27.63 

40.99 

29.50 

1.87 


Calculated  for 
CsAuBr*. 

20.45 
30.34 
49.21 


Calculated  for 
RbAuCl*. 

20.14 
46.46 
33.40 

Calculated  for 
RbAuBr4. 

14.18 
32.73 
53.08 


*  From  a  separate  product. 


214 


ON  THE  CAESIUM  AND  RUBIDIUM 


Crystallography. 

The  crystallization  of  CsAuCU,  CsAuBr4,  RbAuCl4,  and 
RbAuBr4  is  monoclinic.  The  four  salts  form  an  isomorphous 
group  and  are  identical  in  crystalline  habit.  The  forms  which 
have  been  observed  on  them  are : 


c,  001,  0 
m,  110, 1 

2. 


d,  021,  2-i 

e,  201,  2-1 


/K  /r\ 


771 


m 


The  crystals  are  prismatic  and  are  usually  terminated  by  e, 
Fig.  1.  When  other  faces  are  present,  they  are  always  small,  as 
represented  in  Fig.  2.  The  pyramid  p,  which  is  not  shown  in 
the  figure,  frequently  occurs  as  a  small  face,  replacing  the 
edge  between  d  and  e.  Among  the  crystals  of  CsAuBr4  several 
twins  were  observed,  having  p,  111  as  the  twinning  plane,  Fig. 
3,  while  Fig.  4  represents  a  crystal  of  RbAuBr4  twinned  about 
e,  201.  The  letters  belonging  to  the  parts  in  twin  position  are 
underlined.  Both  kinds  of  twins  are  abnormally  developed,  as 
represented  in  the  figures.  In  all  four  compounds  the  cleav- 
age is  perfect,  parallel  to  the  base. 

The  rubidium  salts,  being  the  most  soluble,  form  readily  in 
large  crystals,  several  centimeters  in  length.  The  chloride, 
especially,  yielded  magnificent  crystals,  which  frequently  were 
only  limited  in  length  by  the  size  of  the  vessel  and  volume  of 
the  solution  containing  them.  The  caesium  salts  are  less  solu- 


CHLORAURATES  AND  BROMAURATES. 


215 


ble  and  were  made  in  small  prisms,  seldom  over  5  mm.  in  length. 
The  crystals  were  frequently  hollow  or  cavernous  at  the  ex- 
tremities; this  was  especially  true  of  the  two  bromides.  The 
faces,  for  the  most  part,  gave  excellent  reflections  of  the  signal 
on  the  goniometer. 

The  axial  ratios  are  as  follows: 


CsAuCl4 

I :  c  =  1.1255  : 1  :  0.7228 
P  =  71°  36' 

BbAuCU 

I :  e  =  1.1954  : 1 :  0.7385 
B  =  75°  32' 


In  the  following  tables  the  angles  which  were  chosen  as 
fundamental  are  marked  by  an  asterisk: 


CsAuBr4 

a :  I :  c  =  1.1359  : 1 :  0.7411 
P  =  70°  24J' 

RbAuBr4 

a:5:c:  =  1.1951: 1:0.7256 

=  76° 


CsAuBr4 


110 


Measured. 

m  A  m,  A  1TO  =  *93°  46' 
m  A  c,  110  A  001  =  77°  36' 
m  A  d,  110  A  021  =  44°  6' 
dA  p,  021  A  Til  =  ... 
d  A  e,  021  A  201  =  *75°  17' 
m  A  e,  TTO  A  201  =  *60°  36' 
c  A  e,  001  A  201  =  64°  20' 


Calculated. 

77°  32' 
44°    7' 


Measured. 

*93°  53' 

Calculated. 

*76°  46' 

... 

43°  23' 

43°  20' 

32°  23' 

75°  31' 

32°  40J' 
75°  59' 

*60°  41' 

•  . 

64°  18' 


m  A  m,  Ke-entrant  angle  of  twin, 

BbAuCl* 


27°  58'      27°  58' 

RbAuBr4 


110 


Measured. 

m  A  m9  JLJLU  A  1TO  =  *98°  21' 
m  A  c,  110  A  001  =  *80°  36' 
m  A  d9  110  A  021  =   ... 
d*  p9  021  A  Til  =   ... 
d  A  e,  021  A  201  =   ... 
m  A  e,  HO  A  201  =  *62°  12' 
c  A  c,  001  A  201  =  60°  4' 
d  A  d,  021  A  021  =  110°  20' 


Calculated. 


59°  59' 
110°    4i 


Measured. 

Calculated. 

*98°  40' 

... 

*81°  30' 

.   .    . 

44°  57' 

45°  12J' 

31°  26' 

31°  35£' 

72°  28' 

72°  26' 

62°    9' 

62°  21*' 

*109°  26' 

55°  42' 

55°  17' 

m  A  m,  Re-entrant  angle  of  twin, 

In  their  axial  ratios  the  two  caesium  salts  are  very  similar, 
as  are  also  the  two  rubidium  salts,  while  the  rubidium  com- 


216 


ON  THE  CESIUM  AND  RUBIDIUM 


pounds  differ  considerably  from  those  of  caesium,  especially  in 
the  relation  of  d  to  the  other  axes  and  in  the  angles  /3.  It  is 
therefore  evident  that  the  replacement  of  one  metal  by  another 
in  these  salts  has  a  considerable  influence  upon  their  form, 
whereas,  as  we  have  shown,  such  a  replacement  in  the  caesium 
and  rubidium  trihalides  has  little  or  no  effect.  There  seems 
to  be  no  regularity  in  the  influence  of  the  replacement  of 
chlorine  by  bromine  in  these  gold  salts,  for  in  the  caesium 
compounds  the  chloride  has  a  slightly  shorter  axis  6  and  a 
greater  angle  fi  than  the  bromide,  while  in  the  rubidium  salts 
exactly  the  reverse  is  true  in  both  cases.  This  unexpected 
relation  between  the  chlorides  and  bromides  has  been  con- 
firmed by  repeating  the  measurements,  especially  of  the  angle 
m  A  c,  using  both  crystal  and  cleavage  faces.  It  is  certain  that 
this  angle  is  about  a  degree  greater  with  the  chloride  than  with 
the  bromide  in  the  caesium  salts,  while  in  the  rubidium  com- 
pounds it  is  about  a  degree  less. 

The  crystallization  of  2CsAuGl4.H2O  is  ortho- 
rhombic.     This  salt  was  repeatedly  made,  but 
only  one  crop  of  crystals  was  obtained  which 
was  suitable  for  measurement.    These  were  thin 
plates,  having  the  habit  shown  in  Fig.  5.     They 
were  not  over  5  mm.  in  length  and  were  only 
a  fraction  of  a  millimeter  thick.     On  removal 
from  the  mother-liquor  or  from  a  moist  atmos- 
phere, the   transparent  plates  rapidly  became 
opaque  and  the  faces  lost  their  lustre,  so  that  only  approximate 
measurements  could  be  obtained. 
The  forms  which  were  observed  are : 


a,  100,  i+ 

b,  010,  Vt 


110, 1 
120,  i-2 


d,  101, 1-t 


The  axial  ratio  is  as  follows : 


:5:c  =  0.625:l:0.24 


CHLORAURATES  AND  BROMAURATES.  217 

The  following  measurements  were  made : 

a  A  m,  100  A  110  =  about  32°         a  A  ft,  100  A  010  =  about  90° 
a  A  n,  100  A  120  =  about  51°         d  A  d,  101  A  T01  =  about  42° 

Under  the  polarizing  microscope  the  crystals  show  parallel 
extinction  and,  in  convergent  light,  an  acute  bisectrix  normal 
to  #,  100.  The  plane  of  the  optical  axes  is  the  base.  The 
divergence  of  the  axes  is  large,  the  hyperbolae  opening  out 
beyond  the  field  of  the  microscope.  The  axes  of  elasticity 
are: 

d  —  t,  I  —  a,  c  =  fc. 

The  double  refraction  is  therefore  positive. 

The  change  which  the  crystals  undergo  when  exposed  to 
dry  air  is  a  molecular  rearrangement,  accompanied  by  loss  of 
water  and  probably  a  change  to  the  anhydrous  salt  which  was 
described  above.  This  rearrangement  is  a  beautiful  sight 
when  studied  with  the  microscope  in  polarized  light.  The 
change  commences  a  few  minutes  after  the  crystals  are  re- 
moved from  the  mother-liquor,  and  in  less  than  ten  minutes 
has  usually  advanced  to  such  an  extent  that  the  crystals  are 
no  longer  transparent.  The  crystals  at  first  show  a  uniform 
action  on  polarized  light ;  then  from  different  parts  of  the 
surface  the  rearrangement,  which  is  marked  by  aggregate 
pokrization,  commences.  It  advances,  shooting  out  in  va- 
rious directions  in  a  manner  resembling  the  growth  of  ammo- 
nium chloride  crystals  under  the  microscope,  until  the  whole 
field  is  covered  and  light  is  finally  no  longer  transmitted. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
April,  1892. 


ON  THE  CAESIUM-MERCURIC  HALIDES.* 

BY  H.  L.  WELLS. 

IT  is  to  be  expected  that  more  complete  series  of  double 
halides  can  be  made  with  caesium  than  with  the  other  alkali 
metals,  because  it  is  the  extreme  member  of  the  potassium 
group  and  the  most  electro-positive  element  known,  and  be- 
cause caesium  double  salts  in  general  are  less  soluble  than  the 
corresponding  compounds  of  the  other  alkali  metals.  A  thor- 
ough study  of  these  compounds  seems  desirable,  since  very 
little  work  has  been  done  in  this  direction,  and  therefore  the 
present  investigation  of  the  caesium-mercuric  chlorides,  bro- 
mides, and  iodides  has  been  undertaken. 

The  following  is  a  complete  list  of  the  previously  described 
mercuric  double  halides  containing  the  alkali  metals  and  am- 
monium, as  far  as  I  have  been  able  to  find  them : 

Na2HgCl4  NH4HgCl8  RbHg2Cl5 

Kb2HgCl,  EbHgCl8  KHg2Cl6.2H20 

Cs2HgCl4  KHgBr8  

(NH4)2HgBr4  NH4HgCl8.pI20  

K2HgBr4  KHg018.H20  (NH4)2Hg8Cl8.4H20 

Na2HgI4  KHgBr8.H20  

K2HgI4  NaHgCl8.HH20  

(NH4)2HgCl4.H20  NH4HgI3.l^H20  (NH4)2Hg9Cl20 

K2HgCl4.H20  KHgI8.liH20  

Kb2HgCl4.2H20  

(NH4)2HgI4.3H20  

The  greater  number  of  these  arrange  themselves  into  two 
types  with  varying  water  of  crystallization  or  with  none. 
There  are  two  compounds  of  a  third  type,  while  the  two  re- 

*  Amer.  Jour.  Sci.,  xliv,  September,  1892. 


THE   CESIUM-MERCURIC  HALIDES.  219 

maining,  more  complicated  salts,  stand  alone.  The  last  two 
were  described  by  Holmes.* 

An  effort  has  been  made  to  make  the  examination  of  the 
cesium-mercuric  salts  very  complete,  but  it  is  not  safe  to  say 
that  every  possible  compound  has  been  prepared,  for  negative 
results  are  uncertain.  It  will  not  be  necessary  to  describe  the 
unsuccessful  experiments  where  mixtures  or  uncertain  prod- 
ucts were  obtained.  It  is  sufficient  to  say  that  other  double 
halides  were  repeatedly  looked  for  in  every  direction,  and 
every  indication  of  a  new  salt  was  followed  up  until  a  homo- 
geneous product  was  obtained  and  analyzed. 

The  following  table  gives  a  list  of  the  salts  that  are  to  be 
described.  One  of  them,  Cs2HgCl4,  has  already  been  prepared 
by  Godeffroy.f 

i.  n.  ra. 

Cs3HgCl5  Cs2HgCl4  CsHgClst 
Cs3HgBr5  Cs2HgBr4  CsHgBr8| 
Cs3HgI5  Cs2HgI4  CsHgI3 
Cs3HgCl3Br2  Cs2HgCl2Br2  CsHgClBr,* 
Cs8HgBr3Ia  Cs2HgBr2I21:  CsHgBrl, 
Cs2HgCl2I2  

IV.  V.  VL 

CsHg2Cl6  CsHg8Clu 

CsHg2Brfi  .... 

Cs2Hg3I8  CsHg2I5  

CsHg2ClBr4  CsHg6ClBr10 

These  salts  confirm  the  composition  of  all  the  previously 
known  alkaline-mercuric  halides,  as  given  in  the  preceding 
table,  except  the  single  compound  (NH4)2Hg9Cl2o.  It  is  ex- 
tremely probable,  however,  that  the  correct  formula  for  this  is 
NH4Hg6Cln,  for  Holmes  obtained  results  slightly  lower  than 
his  theory  in  his  ammonium  determinations,  and  it  would  be 
scarcely  possible  to  distinguish  between  the  two  formulas  by 
analysis,  as  will  be  seen  from  the  following  numbers : 

*  Chem.  News,  v,  351.  t  Berichte,  viii,  9. 

J  These  compounds  are  dimorphous. 


220  THE  CAESIUM-MERCURIC  HALIDES. 

Calculated  for  Calculated  for  ru««,« 

(N^)aHg9ClM.  NH4Hg6CIV  Differences. 

Mercury  .....     70.70  71.00  0.30 

Ammonium  ....       1.41  1.27  0.14 

The  differences  between  the  amounts  of  mercury  and  caesium 
for  the  corresponding  formulas  are  0.80  and  0.85,  so  that  it 
is  evident  that  the  csesium  compound  furnishes  a  far  better 
means  of  determining  the  composition  of  the  salts. 

The  first  type,  Cs8HgHl6,  is  a  new  one.  These  compounds 
are  interesting  as  exceptions  to  Remsen's  law  concerning  the 
composition  of  double  halides.* 

The  salt  Cs2Hg3I8,  although  standing  alone  among  the  cse- 
sium compounds,  is  a  very  well  characterized  body,  and  the 
compound  (NH4)2Hg8Cl8.4H2O,  made  by  Holmes,  belongs  to 
the  same  type. 

The  results  of  the  work  on  the  caesium-mercuric  salts  fulfil 
the  expectations  concerning  the  value  of  csesium  as  a  means  of 
studying  alkaline  double  halides,  for  all  the  previously  discov- 
ered types  have  been  made  with  this  metal,  and  one  besides 
that  had  never  been  discovered. 

Preparation. 

The  compounds  were  made  by  dissolving  mercuric  halides 
in  hot  solutions  of  csesium  halides  and  cooling,  or  in  some 
cases  evaporating  at  ordinary  temperatures,  to  crystallization. 
The  relative  amounts  of  the  two  halides  and  the  dilution  both 
have  an  important  influence  in  determining  the  salt  produced. 
In  most  cases  dilution  with  water  is  equivalent  to  the  addition 
of  mercury,  while  concentration  produces  the  same  effect  as 
the  addition  of  a  csesium  halide.  It  has  been  noticed,  where 
more  than  one  salt  is  deposited  from  a  solution  by  cooling, 
that  the  salts  with  more  mercuric  halides  are  formed  first. 
This  shows  that  cooling  a  solution  may  be  equivalent  to  the 
addition  of  csesium. 

There  are  only  a  few  of  the  salts  that  can  be  recrystallized 
unchanged  from  water,  most  of  them  requiring  the  presence  of 

*  Amer.  Chem.  Jour.,  xi,  296 ;  xiv,  86. 


THE  CAESIUM-MERCURIC  HALIDES.  221 

an  excess  of  caesium  halide,  or  in  two  or  three  cases  mercuric 
halide,  for  their  formation.  Crystallization  from  water  can 
therefore  often  be  used  for  preparing  one  salt  from  another. 

All  the  compounds  were  made  with  solutions  of  the  normal 
salts  without  the  use  of  acids.  Some  of  them  have  been  made 
with  alcoholic  solutions,  but  this  solvent  has  not  been  found 
to  possess  any  advantages  except  for  preparing  CsHg2I6. 

Analytical  Methods. 

The  salts  were  always  carefully  examined  to  be  sure  that 
they  were  not  mixtures.  Many  mixed  crops  of  crystals  were 
obtained,  but  I  am  confident  that  the  products  analyzed  were 
pure.  The  crystals  for  analysis  were  always  quickly  and  thor- 
oughly freed  from  the  mother-liquor  by  pressing  repeatedly 
between  smooth  filter-papers,  and  at  the  same  time  they  were 
crushed  to  remove  included  liquid.  During  this  drying  pro- 
cess the  substances  were  exposed  to  the  air  as  little  as  possible 
to  avoid  any  evaporation  of  the  adhering  liquid  before  its 
removal.  After  the  products  had  been  dried  as  thoroughly  as 
possible  in  this  way,  they  were  usually  exposed  to  the  air  for 
an  hour  or  two  to  remove  the  last  traces  of  moisture,  but  this 
was  not  done  in  a  few  cases  where  I  wished  to  be  certain  that 
no  easily  lost  water  of  crystallization  was  present. 

Portions  of  about  one  gram  of  substance  were  usually  taken 
for  analysis.  In  no  case  was  the  analysis  hampered  from  kck 
of  material.  The  chlorides  and  bromides  were  readily  dis- 
solved in  water,  but  it  was  necessary  in  analyzing  the  iodine 
compounds  to  dissolve  them  in  water  containing  alcohol. 
Mercury  was  invariably  determined  as  sulphide,  the  precipitate 
being  collected,  dried  at  100°,  and  weighed  on  an  asbestos  filter 
in  a  Gooch  crucible.  Caesium  was  usually  determined  in  the 
filtrate  from  the  mercuric  sulphide  and  was  always  weighed  as 
sulphate.  In  this  operation  the  excess  of  sulphuric  acid  was 
removed  by  ignition  in  a  current  of  air  containing  ammonia, 
as  suggested  by  Kriiss  for  potassium  sulphate.  In  some  cases 
where  caesium  alone  was  to  be  determined,  the  substance  was 
weighed  out  directly  into  a  platinum  crucible,  sulphuric  acid 


222  THE   CAESIUM-MERCURIC  HALIDES. 

was  added,  the  excess  of  this  and  the  mercury  were  removed 
by  evaporation  and  heating,  and  normal  caesium  sulphate  was 
weighed.  The  halogens  were  invariably  determined  in  sep- 
arate portions  and  were  weighed  as  silver  salts.  In  the  cases 
where  two  were  present,  they  were  determined  by  heating  the 
mixed  silver  halides  to  constant  weight  in  chlorine. 

The  Double  Chlorides. 

These  are  all  white  in  color  and  are  permanent  when  ex- 
posed to  the  air.  On  recrystallizing  from  water  all  of  them 
finally  yield  CsHgCl8. 

Cs&Hg  Cls  is  made  by  dissolving  a  comparatively  small  quan- 
tity of  mercuric  chloride  in  a  nearly  saturated  csesium  chloride 
solution.  It  is  deposited  on  cooling,  but  the  best  crystals  are 
obtained  by  spontaneous  evaporation.  If  too  much  of  the 
mercuric  compound  is  added  or  if  too  much  water  is  present, 
other  double  salts  or  mixed  products  will  be  obtained.  On  the 
other  hand,  if  too  little  mercuric  chloride  is  present,  csesium 
chloride  crystallizes  out.  The  limits  of  the  conditions  under 
which  it  is  formed  are  narrow,  but  by  repeated  trials,  with 
slight  variations  suggested  by  previous  results,  a  pure  product 
is  readily  obtained.  It  forms  slender,  radiating  prisms  which 
are  easily  distinguished  from  the  compounds  with  which  it  is 
liable  to  be  mixed. 

The  following  analysis  was  made  of  a  sample  which  was 
rapidly  dried  on  paper,  but  not  air-dried.  The  small  amount 
of  water  found  was  probably  simply  moisture.  It  was  deter- 
mined by  direct  weighing  in  a  calcium-chloride  tube. 

,,       ,  Calculated  for 

Cs3HgCl6. 

Caesium     .     .     .    51.15  51.38 

Mercury    .     .    .     24.84  25.76 

Chlorine    .     .     .    21.79  22.86 

Water       .    .     .      1.69  0.00 

99.47  100.00 

CsJIgCli  is  produced,  by  cooling  a  hot  solution,  when  a 
little  more  mercuric  chloride  or  water  is  used  than  in  the  case 


THE   CESIUM-MERCURIC  HALIDES.  223 

of  the  last  salt.  The  conditions  for  its  formation  are  narrow. 
It  forms  large  but  usually  very  thin  plates,  which  are  readily 
distinguished  from  the  other  double  chlorides.  A  sample  was 
dried  on  paper  for  analysis. 


Osium     .     .     .     44.06  43.75 

Mercury    ......  32.90 

Chlorine    .     .     .     22.87  23.35 

Water  ....      0.52  0.00 

100.00 

is  dimorphous,  forming,  according  to  circumstan- 
ces, cubic  or  orthorhombic  crystals.  The  cubic  form  is  pro- 
duced under  widely  varying  conditions  by  cooling  dilute 
aqueous  solutions,  when  caesium  chloride  is  considerably  in 
excess.  The  orthorhombic  form  is  deposited  when  caesium 
chloride  is  not  in  great  excess,  and  by  one  or  more  recrystal- 
lizations  from  water  of  all  the  double  chlorides.  This  form 
can  be  recrystallized  from  water  indefinitely. 

The  compound  is  practically  insoluble  in  absolute  alcohol, 
but  it  dissolves  in  alcohol  diluted  with  about  one-third  of  its 
volume  of  water,  and  it  is  remarkable  that  the  cubic  form  is 
deposited  from  such  a  solution  on  cooling. 

The  cubes  often  form  peculiar  aggregates,  apparently  of  a 
pyramidal  shape.  The  orthorhombic  crystals  are  very  brilliant 
and  highly  modified,  usually  forming  groups  of  spear-shaped 
individuals  joined  end  to  end. 

Three  samples  were  analyzed:  A,  cubes  simply  dried  on 
paper;  B  cubes  from  alcohol;  C,  orthorhombic  crystals,  air- 
dry. 

Calculated  for 
T  CsHgCl,. 


Caesium     .    .    .    30.29  30.26  29.92  30.26 

Mercury    .     .     .    44.80  .  .  .  45.63  45.51 

Chlorine    .     .     .    23.40  .  .  .  24.03  24.23 

Water       .    .    .      1.42  .  .  .  J_LI_  0.00 

99.91  99.58  10OOO 


224  THE   CESIUM-MERCURIC  HALIDES. 

Since  the  orthorhombic  form  of  this  compound  is  not  de- 
composed by  water,  its  solubility  could  be  determined.  This 
was  done  by  analyzing  the  mother-liquor  from  a  third  recrys- 
tallization  at  about  17°.  Of  this  solution,  100  parts  contained 
0.4255  parts  of  caesium,  corresponding  to  1.406  parts  of 
CsHgCls. 

CsHgtCh  was  made  by  dissolving  24  g.  of  CsHgClg  and  16  g. 
of  HgCl2  (a  little  more  than  one  molecule  of  the  latter)  in 
about  150  c.  c.  of  hot  water  and  cooling.  A  large  crop  of 
needles  was  obtained  which  were  undoubtedly  homogeneous. 

Analysis  gave  *%$£&?* 

Cesium     .     .    .    18.13  18.72 

Mercury    .     .     .     56.32  56.30 

Chlorine    .    .    .    24.68  24.98 

99.13  100.00 

The  salt  is  not  very  readily  decomposed  by  water,  but  by 
repeated  recrystallization  the  orthorhombic  form  of  CsHgCl3 
is  obtained. 

CsHg&Cln  was  prepared  by  making  a  nearly  saturated  solu- 
tion of  12.5  g.  of  HgCsCla  and  38.5  g.  of  HgCl2  (about  one 
molecule  of  CsCl  to  six  of  HgCl2)  in  boiling  water  and  cool- 
ing. The  compound  was  obtained  in  prisms,  so  well  formed 
that  there  was  no  doubt  about  their  homogeneity.  Two  crops 
were  analyzed. 

,,       ,  Calculated  for 

CsHg6Clu. 

Caesium     .     .      8.68  8.51  8.73 

Mercury    .     .     65.59  .  .  .  65.64 

Chlorine    .     .     24.97  .  .  .  25.63 

99.24  100.00 

A  single  recrystallization  of  this  salt  from  water  gave  a 
mixed  crop  of  crystals,  and  this,  on  repeating  the  operation, 
gave  CsHg2Cl6,  still  containing  a  little  of  the  original  com- 
pound. This  last  crop  was  analyzed. 


Found. 


Calculated  for 
CsHgjCl5. 


Caesium  15.57  18.72 


THE   CESIUM-MERCURIC  HALIDES.  225 

The  Double  Bromides. 

All  of  these  salts  are  white,  or  nearly  so,  except  CsHgBr8, 
which  has  a  lemon-yellow  color.  This  color  is  remarkable, 
since  CsBr  and  HgBr2  are  both  pure  white. 

All  of  the  double  bromides  yield  CsHg2Br5  on  recrystallizing 
them  one  or  more  times  from  water.  It  is  to  be  noticed  that 
this  salt  belongs  to  a  different  type  from  the  double  chloride 
which  is  stable  with  water,  but  if  alcohol  is  used  for  recrys- 
tallizing this  bromide,  the  salt  corresponding  to  the  chloride 
just  mentioned  is  deposited. 

CszHgBr^ — The  preparation  of  this  salt  is  exactly  analogous 
to  that  of  the  corresponding  chloride,  and  it  has  the  same 
appearance. 

Found  Calculated  for 

CssHgBrB. 

Caesium     .     .     .     39.83  39.94 

Mercury    .     .     .     19.50  20.02 

Bromine    .     .     .    39.60  40.04 

98.93  100.00 

CszHgBr^  is  prepared  similarly  to  the  chloride,  but  the 
limits  of  the  conditions  under  which  it  is  formed  are  much 
wider.  Like  the  chloride  it  usually  forms  very  thin  plates, 
but  they  can  sometimes  be  produced  of  sufficient  thickness  for 
measurement.  Three  separate  crops,  made  under  considerably 
different  conditions,  were  analyzed. 


Caesium 

Mercury 

Bromine 


Found. 

Calculated  for 
Cs2HgBr4. 

33.84 

33.84 

34.43 

33.69 

25.68 

25.11 

25.45 

25.45 

40.48 

40.40 

40.52 

40.71 

100.00 

99.94 

99.66 

100.00 

.  —  This  compound  is  dimorphous,  but  while  one 
form  is  cubic,  like  one  of  the  chlorides,  the  other  is  mono- 
clinic  and  has  no  apparent  relation  to  the  orthorhombic 
chloride.  Just  as  in  the  case  of  the  chlorides,  the  cubic  form 
is  produced  when  an  excess  of  the  caesium  halide  is  present, 
while  the  second  form  is  deposited  when  this  excess  is  not  as 

15 


226  THE   CAESIUM-MERCURIC  HALIDES. 

great.  Unlike  the  corresponding  chloride,  the  second  form  of 
the  bromide  is  decomposed  by  reciystallization  from  water,  the 
salt  CsHg2Brs  being  formed,  but,  as  will  be  noticed  beyond, 
the  opposite  transformation  can  be  produced  by  recrystallizing 
the  last-mentioned  salt  from  alcohol.  The  limits  of  formation 
of  the  cubic  salt  are  wide,  but  it  is  difficult  to  produce  the 
other  form  in  a  pure  state,  and  it  is  possible  that  the  mono- 
clinic  crystals  analyzed  were  mixed  with  a  small  quantity  of 
the  cubes. 

Found.  Calculated  for 

Cubic^ Monoclink  CsHgBr9. 

Cesium    .     .     .    23.18  22.89  23.21 

Mercury  .     .     .    34.95  35.54  34.90 

Bromine  .     .     .     41.70  41.63  41.89 

99.83  100.06  100.00 

CsHg^Br^  —  The  recrystallization  of  any  of  the  other 
double  bromides  from  water  produces  this  salt,  and  it  can  be 
recrystallized  indefinitely  without  decomposition.  It  forms 
very  small,  thin  plates  which  have  a  very  faint  tinge  of  yellow. 
By  spontaneous  evaporation  of  a  mother-liquor  from  a  recrys- 
tallization of  this  salt  somewhat  larger  crystals  were  formed. 
Three  separate  crops  were  analyzed. 

Found.  Calculated  for 

, * s          CsHg2Br6. 


jium  .    .     .     14.60  14.69        13.24  14.26 

Mercury  .     .     .     42.71  ......  42.87 

Bromine  .    .    .     42.55  ......  42.87 

99.86  100.00 

The  mother-liquor  from  a  third  recrystallization  from  water 
at  about  16°  was  found  to  contain  0.1151  per  cent  of  caesium, 
corresponding  to  solubility  of  0.807  parts  of  CsHg2Br5  in  100 
parts  of  the  solution.  The  salt  dissolves  rather  sparingly  in 
hot,  strong  alcohol  and,  on  cooling  this  solution,  the  compound 
CsHgBr8  separates  out. 


Caesium    .    .    .    22.68  23.21 


THE   CAESIUM-MERCURIC  HALIDES.  227 

The  crystals  thus  obtained  were  not  large  enough  to  measure, 
but  it  was  probable,  from  microscopic  examination,  that  they 
were  the  monoclinic  form  of  this  compound.  This  is  interest- 
ing from  the  fact  that  it  is  the  cubic  form  of  CsHgClj  which 
crystallizes  from  alcoholic  solutions. 

No  satisfactory  crops  of  crystals  were  obtained  from  solu- 
tions made  with  CsHg2Cl6  and  HgBr2,  together. 

The  Double  Iodides. 

These  salts  are  all  yellow,  CsHg2I2  and  Cs2Hg8I8  having  a 
color  nearly  like  that  of  normal  potassium  chromate,  while  the 
others  become  paler  as  the  csesium  chloride  increases.  All  of 
them  are  decomposed  by  water,  forming  compounds  containing 
more  mercuric  iodide  than  the  original  salt,  or,  at  last,  mercuric 
iodide  itself.  It  is  therefore  possible  to  take  any  one  of  these 
double  salts,  and,  by  recrystallizing  from  water  and  evaporating 
the  resulting  solutions,  to  prepare  the  complete  series  of  five 
double  iodides,  as  well  as  the  component  simple  iodides,  with- 
out the  use  of  any  new  material.  It  is  noticeable  that  the 
iodides  differ  from  the  chlorides  and  bromides  in  not  including 
a  salt  that  can  be  recrystallized  continually  from  water.  This 
peculiarity  is  doubtless  due  to  the  comparative  insolubility  of 
mercuric  iodide.  In  most  cases  the  analyses  of  the  salts  con- 
taining iodine  show  an  excess  of  mercury  and  a  deficiency  of 
the  halogen  (or  halogens).  It  is  not  known  whether  this  was 
due  to  some  impurity  in  the  salts  or  to  analytical  errors.  It  is 
not  considered  probable  that  inaccuracies  in  the  analyses  could 
have  caused  so  much  variation  from  theory,  for  the  methods 
used  were  the  same  as  for  the  chlorides  and  bromides,  except 
that  alcohol  was  used  as  a  solvent,  and,  while  halogens  and 
mercury  were  always  determined  in  separate  portions,  the 
summations  of  the  analyses  were  usually  satisfactory. 

C8sHgI5.  —  This  salt,  like  the  corresponding  chloride  and 
bromide,  requires  for  its  preparation  a  very  concentrated  solu- 
tion of  the  csesium  halide  containing  a  relatively  small  amount 
of  the  mercuric  compound.  It  crystallizes  well  and  may  be 


228  THE   CAESIUM-MERCURIC  HALIDES. 

obtained  either  by  cooling  or  spontaneous  evaporation.    The 
crystals  form  peculiar,  steep  pyramids. 


Vn      *  Calculated  for 

Found' 


Caesium    .    .    .    33.02  32.33 

Mercury    .     .     .     16.33  16.21 

Iodine  ....     50.42  51.46 

99.77  100.00 

Its  specific  gravity,  taken  in  benzol,  was  found  to  be  4.605. 

When  this  salt  is  dissolved  in  a  small  quantity  of  hot  water, 
the  compound  Cs2HgI4  crystallizes  out  on  cooling,  but  with  a 
larger  quantity  of  water  everything  remains  in  solution. 

CszHgIi.  —  This  salt  is  produced  under  wide  limits  of  condi- 
tions by  cooling  solutions  of  the  component  salts  when  caesium 
iodide  is  in  excess.  The  monoclinic  crystals  vary  in  habit, 
forming  long  prisms,  nearly  square  plates  or  intermediate 
forms.  They  are  often  obtained  of  very  large  size,  sometimes 
extending  completely  across  the  bottom  of  the  vessel  contain- 
ing the  solution  and  turning  upward  at  the  ends  besides. 


Caesium 
Mercury 
Iodine . 


Two  determinations  of  the  specific  gravity,  taken  in  benzol, 
gave  the  numbers  4.799  and  4.812. 

The  salt  is  decomposed  by  water,  giving,  according  to  the 
quantity  used,  either  one  of  the  salts  containing  more  mercuric 
iodide  or  mercuric  iodide  itself.  It  is  not  dissolved  or  decom- 
posed by  alcohol. 

CsHgl^.H*  Of). —  This  salt  is  formed  only  within  very  nar- 
row limits  from  solutions  containing  a  little  more  mercuric 
iodide  or  water  than  those  from  which  the  preceding  salt  is 
obtained.  These  conditions  are  perhaps  most  easily  reached 
by  dissolving  the  last  salt  in  a  small  amount  of  hot  water  and 
cooling.  It  often  happens  that  the  three  salts  Cs2Hg3I8, 


Pound. 

27.32        27.39 

Calculated  for 
Cs2HgI4. 

27.31 

21.57 

21.21 

20.53 

51.41 

51.49 

52.16 

100.30 

100.09 

100.00 

THE   CAESIUM-MERCURIC  HALIDES.  229 

CsHglg,  and  Cs2HgI4  are  successively  deposited  as  a  solution 
cools,  and  it  is  consequently  difficult  to  obtain  the  salt  under 
consideration  in  a  pure  state,  but  this  was  accomplished  after 
a  great  many  trials  with  varying  conditions.  The  compound 
forms  very  thin  transparent  plates  which  usually  radiate  from 
a  point  and  are  often  of  large  size.  By  pressing  on  paper  they 
rapidly  become  opaque.  Whether  this  is  caused  by  molecular 
rearrangement  or  loss  of  water  of  crystallization  is  not  certain, 
for,  on  account  of  the  extreme  thinness  of  the  crystals,  it  was 
impossible  to  decide  whether  a  small  amount  of  moisture  or  a 
molecule  of  very  unstable  water  of  crystallization  was  present. 
Two  samples  were  analyzed.  A  was  air-dried  after  pressing 
on  paper ;  B  was  quickly  dried  on  paper. 


Found. 
A. 

Calculated  for 
CeHgl,. 

Found.      C 
B. 

Jalculated  : 

Caesium.   . 

.    18.81 

18.63 

18.25 

18.17 

Mercury  . 

.    29.29 

28.01 

28.74 

27.33 

Iodine 

.    51.50 

53.36 

50.98 

52.05 

Water  .     . 

.  .  . 

0.00 

2.51* 

2.45 

99.60      100.00  100.48      100.00 

Like  all  the  other  iodides,  this  salt  is  decomposed  by  water. 

Cs2Hgsl8  is  formed  under  widely  different  conditions.  It  is 
most  convenient  to  prepare  it  by  dissolving  Cs2HgI4  in  the 
proper  amount  of  hot  water  and  cooling.  It  is  also  formed, 
in  a  finely  divided  condition,  by  treating  the  same  salt  with 
not  too  much  cold  water.  The  crystals  vary  considerably  in 
habit,  but  they  can  be  readily  distinguished  from  the  other 
iodides.  A  characteristic  form  is  a  triangular  plate,  but  plates 
of  different  shape  and  more  or  less  elongated  prisms  often  oc- 
cur. The  following  analyses  were  made  of  separate  crops. 
Sample  C  was  made  by  treating  Cs2HgI4  with  cold  water. 

Found.  Calculated  for 

. A. >  B.  C.  CsjHg8I8 

Cesium     .    .     13.89      .  .  .      14.14  14.07  14.13 

Mercury    .     .     33.76      33.83  31.88 

Iodine  .     .     .    52.07    52.10      52.63  52.96  53.99 

99.72  100.86  100.00 
*  By  loss  at  100°. 


230  THE   CAESIUM-MERCURIC  HALIDES. 

Specific  gravity,  taken  in  benzol,  5.14.  The  salt  dissolves 
in  alcohol.  It  is  decomposed  by  water  with  the  separation  of 
a  part  of  the  mercuric  iodide.  From  the  solution  thus  ob- 
tained, the  salts  containing  less  mercuric  iodide  can  be  pre- 
pared by  evaporation. 

CsHff2T&.  —  When  a  hot  aqueous  solution  of  caesium  iodide 
is  saturated  with  mercuric  iodide,  this  compound  is  formed  on 
cooling,  but,  under  these  conditions,  the  substance  is  usually 
mixed  with  HgI2  and  often  with  Cs2Hg3I8.  When  weak  alco- 
hol is  used  as  a  solvent,  however,  a  pure  product  is  obtained 
without  difficulty.  It  forms  slender  yellow  prisms  which  be- 
come red  on  standing  in  an  aqueous  mother-liquor.  They  are 
more  permanent  in  the  solution  when  it  is  alcoholic,  but,  on 
drying  them  by  pressing  on  paper,  they  quickly  assume  the 
red  color  of  mercuric  iodide  without  losing  their  form.  It  is 
probable  that  the  spontaneous  decomposition  results  in  the 
formation  of  Cs8HgaI8  and  HgI2.  It  was  necessary  to  analyze 
the  material  which  had  become  red. 

,,       ,  Calculated  for 

Found. 


Csesium    ....     11.47  11.39 

Mercury  ....    35.73  34.25 

Iodine  .....    52.93  54.36 

100.13  100.00 


The  Mixed  Double  Halides. 

A  great  deal  of  labor  has  been  devoted  to  a  study  of  these 
compounds  in  order  to  find  to  what  extent  they  could  be  pre- 
pared. The  results  show  that  caesium  chloride  and  mercuric 
bromide  unite  readily,  although  there  is  a  tendency  towards  an 
exchange  of  halogens  and  the  formation  of  unmixed  salts.  It 
is  also  noteworthy  that,  while  there  is  a  double  chloride  as  well 
as  a  double  bromide  which  is  not  decomposed  by  recrystalliza- 
tion  from  water,  all  the  chloro-bromides  finally  yield  mercuric 
bromide  when  so  treated. 

The  number  of  bromo-iodides  is  less  than  that  of  the 
unmixed  salts,  for,  when  attempts  are  made  to  prepare  com- 


THE   CESIUM-MERCURIC  HALIDES.  231 

pounds  containing  the  larger  amounts  of  mercuric  iodide, 
there  is  an  exchange  of  halogens  and  almost  pure  double 
iodides  are  produced. 

Only  one  compound  of  mercuric  iodide  with  caesium  chlo- 
ride could  be  prepared.  This  is  CsaHgCl2I2,  and  the  type  to 
which  it  belongs  may  probably  be  considered,  on  this  account, 
the  most  stable  one  of  the  csesium-mercuric  halides. 

It  is  evident  that  the  mixed  salts  are  not  as  readily  formed 
as  the  unmixed,  and  that  the  more  dissimilar  the  two  halogens 
are,  the  less  tendency  there  is  to  form  the  mixed  compounds.* 

In  preparing  these  salts,  containing  two  different  halogens, 
the  halogen  of  higher  atomic  weight  was  always  added  in 
combination  with  the  mercury.  The  methods  of  preparation 
are  exactly  analogous  to  those  by  which  the  unmixed  salts 
are  made,  so  that  most  of  these  details  will  be  omitted  in 
describing  them. 

The  Chloro-bromides. 

In  form  these  all  resemble  the  unmixed  salts  between  which 
they  are  intermediate,  and  all  of  them  are  colorless  except 
CsHgClBr2,  which  is  pale  yellow. 


Calculated  for 
CS8HgCl,Br8. 

Osium    ....    48.12  46.10 

Mercury   ....     23.80  23.11 

Chlorine  ....     16.24  12.30 

Bromine  ....    11.82  18.49 

99.98  ioOjW 

The  product  was  made  with  a  very  large  excess  of  caesium 
chloride,  and  it  contained  a  considerable  amount  of  the  double 
chloride.  The  analysis  corresponds  nearly  to  the  formula 
2Cs3HgCl3Br2  +  CssHgCl6. 

O82HgClzBr2.  —  Two  products,   which    were  made  under 
different  conditions,  were  analyzed. 

*  This  point  is  discussed  in  connection  with  the  caesium  trihalides.    (Wells 
and  Penfield,  Amer.  Jour.  Sci.,  Ill,  xliii,  31  and  32.) 


232 


THE   CESIUM-MERCURIC  HALIDES. 


Found. 


Caesium  . 
Mercury  . 
Chlorine  . 
Bromine  . 


40.34 
28.79 
12.94 
17.43 


38.86 
28.58 
10.48 
22.07 


99.50        99.99 


Calculated  for 
Cs2HgCl2Bra. 

38.16 
28.69 
10.19 
22.96 
100.00 


One  of  these  crops  corresponds  very  closely  to  the  formula, 
while  the  other,  made  in  the  presence  of  a  greater  excess  of 
caesium  chloride,  contains  a  little  Cs2HgCl4. 

CsHgClBrz.  —  This  has  been  obtained,  like  the  chloride  and 
bromide,  in  dimorphous  forms.  One  of  these  is  cubic  like  the 
other  salts,  while  the  second  form  crystallizes  like  the  chloride 
and  not  like  the  bromide.  The  color  of  both  varieties  is  pale 
yellow. 

Found. 


Cubic  Form. 

Orthorhombic  Form. 
Separate  Products. 

Calculated  for 
CsHgClBr2. 

Caesium   . 

,    26.50 

26.97 

26.74 

26.01 

25.17 

Mercury  . 

.    38.75 

40.21 

40.05 

38.91 

37.84 

Chlorine  . 

.      9.23 

11.32 

11.42 

8.53 

6.72 

Bromine  . 

.    25.21 

21.63 

21.94 

26.65 

30.27 

99.69 

100.13 

100.15 

100.10 

100.00 

These  products  evidently  contain  some  of  the  chloride. 
The  analyses  of  the  first  two  samples  of  the  orthorhombic  salt 
correspond  closely  to  the  formula,  2CsHgClBr2  +  CsHgCl3. 

CsHg2  ClBr±.  —  Two  separate  products,  made  under  different 
conditions,  were  analyzed. 


Caesium 
Mercury 
Chlorine 
Bromine 


Found. 

15.48  15.23 

45.72  45.06 

5.75  3.71 

32.30  _36.06 

99.25  100.06 


Calculated  for 
CsHg2ClBr4. 

14.97 

45.02 

3.99 

36.02 

100.00 


—  This  compound  was  prepared  by  recrystal- 
lizing  the  preceding  salt  from  water. 


THE   CESIUM-MERCURIC  HALIDES.  233 

f,       •,  Calculated  for 

C8Hg5ClBr10. 

Caesium     .    .    .      6.23  6.76 

Mercury   .     .     .    52.77  50.80 

Chlorine  .     .     .      2.85  1.80 

Bromiue   .    .    .    38.19  40.64 

100.04  100.00 

There  is  a  chloride  corresponding  to  this  compound,  but  no 
bromide  was  obtained  of  this  type.  It  forms  elongated  crys- 
tals, much  smaller  than  the  chloride.  The  final  product,  when 
this  salt  is  recrystallized  from  water,  is  mercuric  bromide. 

The  Bromo-iodides. 

Only  three  of  these  compounds  have  been  prepared.  When 
attempts  were  made  to  obtain  compounds  containing  larger 
amounts  of  mecuric  iodide,  there  was  an  interchange  of  halo- 
gens and  nearly  pure  double  iodides  were  formed.  Two  such 
products  were  analyzed. 

Found.  Calculated  for  Found  Calculated  for 

Us2Ug3l8.  (JsJtlg2l5. 

Caesium    .    .     .    14.69  14.13  11.62  11.39 

Mercury   .     .     .    33.72  31.88  36.09  34.25 

Bromine   .     .     .      2.19  0.00  2.43  0.00 

Iodine  ....    49.58  53.99  49.45  54.36 

100.18  100.00  99.59  100.00 

Cs^HgBr^Iz.  —  This  salt  resembles  the  iodide,  not  the  bro- 
mide, in  form.  Its  color  is  a  pale  yellow,  intermediate  between 
the  brighter  iodide  and  the  colorless  bromide. 


Caesium     .     .     .    37.21  36.50 

Mercury    .    .    .     19.39  18.30 

Bromine    .     .     .     25.18  21.96 

Iodine  ....     18.24  23.24 

100.02  100.00 

.  —  This  compound  has  a  very  faint  tinge  of 

yellow.     It  is  apparently  dimorphous,  although  no  other  salt 


234  THE   CAESIUM-MERCURIC  HALIDES. 

of  this  type  has  been  made  in  more  than  one  form.  It  occurs 
in  very  thin  plates,  like  the  chloride,  bromide,  and  chloro- 
bromide,  and  in  stout  monoclinic  crystals  like  the  iodide. 
The  limits  of  the  conditions  under  which  the  plates  are  made 
are  very  narrow,  and  it  is  difficult  to  obtain  them  free  from 
the  dimorphous  crystals.  As  the  solution  cools,  however,  the 
plates  are  deposited  first,  and,  with  the  proper  dilution,  it  is 
possible  to  remove  them  and  get  the  mother-liquor  pressed  out 
with  paper  before  the  other  crystals  begin  to  form.  There 
is  no  difficulty  in  preparing  the  other  modification  of  the 
compound. 

Found. 


m,.    T>lofoo        Orthorhombic       Calculated  for 
Thin  Plates.  Crystals.  Cs.,HgBr2I2. 

Cesium    .     .    .    30.71  30.20  30.23 

Mercury  .     .    .    24.14  23.86  22.73 

Bromine  .    .    .    21.05  17.91  18.18 

Iodine.     .    .    .     24.23  28.50  28.86 

100.13  100.47  100.00 

It  is  noticable  that  the  plates,  which  resemble  the  bromide 
in  form,  contain  a  small  excess  of  bromine  and  a  correspond- 
ing deficiency  of  iodine. 

CsHgBrli.  —  Only  one  form  of  this  compound  has  been 
prepared,  although  three  other  salts  of  this  type  are  dimor- 
phous. Its  form  is  monoclinic,  like  one  modification  of  the 
bromide,  and  it  is  pale  yellow  in  color. 

,,       ,  Calculated  for 

Found.  CsHgBrI2. 

Caesium     .    .     .    20.26  19.94 

Mercury    .     .     .     31.44  29.99 

Bromine    .     .     .     13.35  11.99 

Iodine  ....    34.39  38.08 

99.44  100.00 

The  Chloro-iodide,  CszHg  012I2. 

This  is  the  only  combination  of  caesium  chloride  and  mer- 
curic iodide  that  could  be  produced.  It  is  formed  only  in 
very  concentrated  solutions  containing  a  great  excess  of 


THE   CAESIUM-MERCURIC  HALIDES.  235 

caesium  chloride.  Its  form  is  different  from  any  other  salt  of 
the  type,  for  it  occurs  in  slender,  radiating  needles.  It  is 
snow-white  in  color,  and  when  it  is  brought  in  contact  with 
water  it  instantly  becomes  bright  red  from  the  formation  of 
mercuric  iodide.  Two  entirely  separate  crops  were  analyzed. 


Found. 

Caesium    .     .     .    33.38  33.14  33.63 

Mercury   .     .     .    26.71  .  .  .  25.28 

Chlorine  .     .     .       8.87  9.01  8.98 

Iodine.     .     .    .    30.85  30.17  32.11 

99.81  100.00 

When  it  was  attempted  to  make  a  chloro-iodide  containing 
more  mercuric  iodide  than  this,  a  nearly  pure  double-iodide 
was  formed  by  exchange  of  halogens. 

Calculated  for 


Csesium  .  .  .  13.76 
Mercury  .  .  .  33.49 
Chlorine  .  .  .  0.16 
Iodine  ....  50.74 
98.15 

The  investigation  of  double  halides  will  be  continued  hi  this 
laboratory,  and  it  is  hoped  that  a  further  study  of  the  caesium 
salts  will  lead  to  a  better  knowledge  of  this  class  of  compounds 
in  general  than  we  now  possess. 

In  conclusion,  it  gives  me  pleasure  to  express  my  gratitude 
to  my  colleague,  Professor  Penfield,  for  his  hearty  co-operation 
in  undertaking  the  crystallographic  examination  of  the  com- 
pounds which  have  been  described.  His  results  have  been 
freely  used  in  the  foregoing  descriptions,  and  they  will  be 
given  in  detail  in  a  future  article. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
May,  1892. 


ON  THE   CRYSTALLOGRAPHY  OF  THE   CESIUM- 
MERCURIC   HALIDES.* 

BY  S.  L.  PENFIELD. 

THE  salts  to  be  described  in  this  paper  were  prepared  by 
Prof.  H.  L.  Wells,  and  their  chemical  description  has  been 
given  by  him  in  the  preceding  paper. 

The  crystals  were  all  measured  on  a  Fuess  reflecting  goni- 
ometer, model  II,  and  great  pains  were  taken  to  select  the  best 
measurements  as  fundamental.  In  a  few  cases,  where  the 
crystals  were  very  small  and  the  reflections  of  the  signal, 
therefore,  rather  broad,  the  mean  of  a  series  of  measurements 
was  used.  The  axial  ratios  are  given  in  tabular  form  at  the 
beginning  of  each  separate  chemical  type,  and  the  fundamental 
angles,  from  which  these  are  derived,  are  marked  by  an  asterisk 
in  the  table  of  angles  accompanying  each  salt. 

Type  3  :  1. 

&   :    b    :   c 
0.7976  : 1 : 0.6605 
0.7882  : 1 :  0.6527 
0.7966  : 1 :  0.6656 
0.5362  : 1 :  0.97975 
0.8043:1:0.6532 
Approx.  like  Cs3HgI5 

The  first  three  salts  have  exactly 
the  same  habit  and  crystallize  in 
slender  prisms,  attached  at  one 
end  and  terminated  at  the  other 
by  faces  which  are  arranged  with 
monoclinic  symmetry,  Figs.  1,  2, 
and  3.  The  crystals  were  seldom 
over  1  mm.  in  diameter,  but  the 
faces  were  perfect  and  admitted  of 


Cs8HgCl6 
Cs3HgCl3Br2 
Cs8HgBr6 
Cs8HgI6 

Cs3HgBr8I2 
1. 


Orthorhombic,  monoclinic  hemihedrism 
Orthorhombic,  monoclinic  hemihedrism 
Orthorhombic,  monoclinic  hemihedrism 
Orthorhombic,  sphenoidal  hemihedrism 
or  f  a  :  b  :  §  c  = 
Orthorhombic,  sphenoidal  hemihedrism 


m 


m 


771 


accurate  measurement.     The  forms  and  angles  are : 

*  Amer.  Jour.  Sci.,  xliv,  October,  1892. 


CESIUM-MERCURIC  HALIDES.  237 

m,  110, 1  d>,  OT1,  '1-T  jp,  111,  1 

d,  on,  i-r         6, 021, 2-r  y,  ITI,  a 

Measured.  Calculated.  Measured.   cWiilated.  Measured!3  Calculated. 

m  A  m,  110  A  110  =  *77°    9'  ...  76°  33'    76°  30'  *77°    5'      ... 

m  A/),  HO  A  111  =  *43°  21'  ...  *43°  29'       ...  *43°    6£'     ... 

m  AP,  110  A  111=   80°  41X  80°41i'  80°  37'    80°  36$' 

m  A  d,  110  A  Oil  =   69°  55'  69°  54'  70°  14'    70°  13'        69°  49'    69°  48' 

m  A  e,  110  A  021  =   60°    8'  60°  11'  60°  10'    60°    7' 

d  A  e,  Oil  A  021  =   19°  29'  19°  26'  19°  28'    19°  25'           

d  A  d',011  A  Oil  =   66°  53'  66°  63$'  *66°  16'       ...           67°  16'    67°  18' 

d  A/>,  Oil  A  111  =  34°  39'  34°  39'  34°  37'    34°  44'        34°  47'    34°  4^ 

The  crystals  have  orthorhombic  optical  properties.  When 
lying  on  their  prismatic  faces  all  show  in  polarized  light  an  ex- 
tinction parallel  to  the  vertical  axis,  and  in  convergent  light  a 
trace  of  the  ring  system  can  be  seen,  indicating  that  the  plane 
of  the  optical  axes  is  the  base. 

We  have  here  an  excellent  illustration  of  monoclinic  hemi- 
hedrism  in  the  orthorhombic  system.  Among  all  of  the  crystals 
which  were  examined,  there  was  not  one  which  had  a  holo- 
hedral  termination.  The  forms  d'  and  p1,  when  present,  were 
always  smaller  than  the  corresponding  forms  d  and  jt?,  while  e 
was  only  observed  to  the  right  above.  Also  the  right-handed 
vertical  edge  of  the  prism  showed  a  tendency  toward  a  skele- 
ton-like growth,  which  was  not  observed  to  the  left.  In 
measuring  the  crystals  great  pains  were  taken  to  detect  a 
monoclinic  character  by  the  angles,  but  none  could  be  found. 
Of  course  the  three  salts  may  be  regarded  as  monoclinic, 
with  an  angle  /3,  differing  so  little  from  90°  that  it  cannot 
be  detected  by  the  goniometer ;  but  against  such  a  supposition 
are  the  arguments  that  the  crystals  have  orthorhombic  optical 
properties,  and  while  there  is  a  variation  in  the  axial  ratios  of 
the  series  as  bromine  is  substituted  for  chlorine,  there  is  no 
change  in  the  angle  &  as  would  be  expected  if  the  salts  were 
monoclinic.  In  this  connection  it  is  interesting  to  note  that 
while  the  chloride  and  bromide  are  very  similar  in  their  axial 
ratios,  the  chemically  intermediate  chloro-bromide  is  not 
crystallographically  intermediate. 


238 


CRYSTALLOGRAPHY  OF  THE 


At  the  present  time  there  seems  to  be  no  other  known 
compound  which  illustrates  this  hemihedrism.  Different  sub- 
stances, which  have  been  referred  to  this  class,  as  datolite 
or  wolframite,  for  example,  have  been  shown  by  accurate 
measurement,  or  a  study  of  their  optical  properties,  to  be  truly 
monoclinic.  Prof.  P.  Groth,  in  the  last  edition  of  his  "  Phy- 
sikalische  Krystallographie,"  has  not  mentioned  this  hemi- 
hedrism as  a  possibility  in  the  orthorhombic  system,  although 
in  the  former  edition  of  his  work  and  in  most  treatises  on 
crystallography  it  is  recognized. 


The  different  crops  of  Cs3HgI6  which  were  examined  showed 
a  great  variety  in  habit,  represented  by  Figs.  4-8.  The  hemi- 
hedral  development  is  not  always  strongly  marked,  and  forms 
like  Figs.  5  and  6  are  the  commonest.  The  crystals  sometimes 
measured  over  5  mm.  in  diameter  and  gave  excellent  reflections. 

Only  one  crop  of  Cs3HgBr3I2  was  examined.  The  crystals 
were  in  the  form  of  sphenoids,  Fig.  9,  some  of  them  over  10  mm. 
in  diameter,  but  the  faces  were  curved  and  striated  and  only 
approximate  measurements  could  be  made. 

The  forms  which  were  observed  are : 
b,  010,  i*        d,  102,  H        s,  021,  2-r 


p 


c,  001,  0  r,  Oil,  1-T       p,  111,  1 

The  angles  of  Cs8HgI5  are  : 


112, 


Measured.     Calculated. 


c   A  p,  001  A  111  =  *64°  15' 

p  A  ;/,  111  A  111  =  *50°  23' 
c  A  r,  001  A  Oil  =  44°  23' 
c  A  s,  001  A  021  =  62°  58' 


44°  25' 
62°  58' 


Measured. 

c  A  o,  001  A  112  =  46°  V 
o  A  o',  112  A  112  =  39°  65' 
o  A  o',  112  A  112  =  87°  57' 
o  A  d,  112  A  102  =  19°  50' 
p  A  e,  111  A  121  =  17°  48' 


121,-2-2 


Calculated. 
46°  2' 
39°  46' 
87°  56' 
19°  53X 
18°  4X 


CAESIUM-MERCURIC  HALIDES.  239 

Both  Cs8HgI6  and  Cs8HgBr8I2  cleave  distinctly,  parallel  to 
the  base,  but  the  crystals  are  very  brittle  and  usually  break 
with  a  conchoidal  fracture.  Crystals  of  the  former,  which  are 
tabular  parallel  to  the  base,  show  in  convergent  polarized  light 
a  bisectrix  normal  to  c,  001 ;  the  plane  of  the  optical  axes  is 
the  macropinacoid,  and  their  divergence  is  large. 

Type  2  :  1. 

a    :    b    :    c 

Cs2HgCl4        Not  measured. 

Cs2HgBr4        Orthorhombic  0.6706  :  1 :  1.4715 

Cs2HgCl2Br2  Orthorhombic  0.567    :  1  :    ... 

Cs2HgCl2I2     Orthorhombic  Not  measured. 

Cs2HgI4  Monoclinic  1.3155:1:0.9260  0  =  69°  56' 

Cs2HgBr2I2     Monoclinic  Approximately  like  Cs2HgI4. 

The  crystals  of  Cs2HgCl4  were  too  thin  to  measure. 

Both  Cs2HgBr4  and  Cs2HgCl2Br2  crystallize  in 
thin  rectangular  plates;  those  of  the  former  were 
sometimes  several  centimeters  long,  but  seldom  over 
J  mm.  thick,  and  had  the  habit  shown  in  Fig.  10. 
The  crystals  of  the  latter  salt  were  very  much 
thinner.  The  plates  were  often  grouped,  with  the 
large  pinacoid  faces  slightly  divergent,  and  isolated 
crystals,  suitable  for  exact  measurement,  were  only 
occasionally  found. 

The  forms  which  were  observed  on  Cs2HgBr4  are : 

ft,  010,  f-r       c,  001,  0       m,  110,  /       d,  Oil,  1-T      j>,  221,  2 


Kg.  10. 


and  on  Cs2HgCl2Br2,  6,  m  and  a  second  prism  130,  i-3.     The 
end  faces  could  not  be  made  out. 

The  angles  of  Cs2HgBr4  are  : 

Measured.  Measured.       Calculated. 

m  A  m,  110  A  1TO  =  *59°  25'  m  A  Pt  110  A  221  =  33°  58  J'  33°  58' 

6  A 


On  this  salt  the  dome  d  is  always  small  and  frequently 
wanting.  The  pyramid  p  was  only  observed  on  a  few  crystals. 
In  convergent  polarized  light  a  bisectrix  may  be  seen  normal 


240  CRYSTALLOGRAPHY  OF  THE 

to  5,  010.  The  plane  of  the  optical  axes  is  the  macropinacoid, 
and  their  divergence  is  so  large  that  they  cannot  be  measured 
in  air,  but  in  <2-monobromnaphtaline  the  following  values  were 
obtained : 

2H  =  80°  12'  for  yellow,  Na  flame. 
2H  =  85°  23'  for  red,  Li  flame. 

The  dispersion  is  strong  p>v.     The  acute  bisectrix  is  axis 
of  least  elasticity,  the  double  refraction  is  therefore  positive. 
The  only  angles  on  Cs2HgCl2Br2  which  were  measured  are : 

m  A  m,  110  A  110  =  *59°  6'  and  110  A  130  =  approx.  30°  53',  calculated  30°  59' 

In  convergent  polarized  light  a  bisectrix  may  be  seen  normal 
to  5,  010.  The  plane  of  the  optical  axes  is  the  macropinacoid, 
and  their  divergence  is  large.  The  axis  of  greatest  elasticity 
is  normal  to  b. 

Only  very  fine  needles  of  Cs2HgCl2I2  were  obtained,  which 
were  too  small  for  measurement.  These  appeared  under  the 
microscope  as  striated  prisms,  with  their  obtuse  edges  rounded 
by  oscillatory  combinations.  In  polarized  light  they  show  a 
parallel  extinction,  and  in  convergent  light  a  biaxial  interfer- 
ence figure,  the  plane  of  the  optical  axes  being  the  vertical 
pinacoid.  The  acute  bisectrix  is  axis  of  least  elasticity. 

The  crystals  of  Cs2HgI4,  which  were  frequently  several  cen- 
timeters in  diameter,  showed  a  variety  of  habits  represented 


13. 


42 


in  Figs.  11,  12  and  13.  The  crystals  of  the  latter  habit  are 
usually  attached  at  one  end  and  taper  toward  the  free  ex- 
tremity, owing  to  a  tendency  to  develop  vicinal  pyramids  in 
the  zone  d-b. 


CAESIUM-MERCURIC  HALIDES. 


241 


The  crystals  of  Cs2HgBr2T2,  which  were 
examined,  were  about  2  mm.  in  diameter  and 
had  the  simple  habit  shown  in  Fig.  14.  The 
faces  were  rounded  and  uneven,  so  that  only 
approximate  measurements  could  be  made. 

The  forms  and  angles  are : 


a,  100,  i-l 

b,  010,  i- 1 


c,  001,  0 
m,  110,  / 


Cs2HgI4. 
Measured.  Calculated. 


c  A  a,  001,  100  =  *69°  56' 

m  A  m,  110  A  T10  =  *77°  58' 

a  A  d,  TOO  A  201  =  *41°  25' 

c  A  e,  001  A  Oil  =  40°  55' 


d,  201,  2-i 

e,  Oil,  14 

Cs,HgBr2I2. 
Measured  approximately. 

66°  41'  to  66°  47' 
77°  16'  to  77°  57' 


41°  V 


The  cleavage  of  both  salts  is  perfect  parallel  to  the  base, 
less  so  parallel  to  the  clinopinacoid.  With  Cs2HgI4  the  plane 
of  the  optical  axes  is  at  right  angles  to  the  symmetry  plane, 
and  clinopinacoid  cleavage  sections  show  in  convergent  polar- 
ized light  an  obtuse  bisectrix,  which  is  axis  of  least  elasticity. 
The  axis  of  greatest  elasticity  makes  an  angle  of  about  50° 
with  the  vertical  axis  in  the  acute  angle  j3. 

Type  1  :  1. 

a    :    b     :     c 

CsHgClg       Isometric  and  Orthorhombic    0.57735  :  1  :  0.40884 
CsHgClBr2  Isometric  and  Orthorhombic    Approximately  like  the  above. 
CsHgBrg      Isometric  and  Monoclinic         1.0124  :  1  :  0.70715     0  =  87°  7' 
CsHgBrLj     Monoclinic  0.978    :  1  :  0.743         0  =  87°  3£' 

CsHglg         Not  measured. 

The  first  three  compounds  are  dimorphous,  and,  from  solu- 
tions containing  an  excess  of  alkali  halide,  they  all  crystallize 
in  cubes.  These  sometimes  have  their  edges  truncated  by 
small  dodecahedron  faces,  less  often  bevelled  by  210,  i-2.  The 
crystals  show  a  slight  action  on  polarized  light  and  give  an 
extinction  parallel  to  the  diagonals  of  the  cube,  but  this 
anomaly  is  probably  due  to  some  internal  tension,  for  when 
crushed  the  fragments  are  isotropic.  No  cleavage  could  be 
detected. 

16 


242  CRYSTALLOGRAPHY  OF  THE 

CsHgCls  was  repeatedly  recrystallized  from  water  and 
always  two  types  were  observed.  One  of  these  was  confined 

to  those   crystals   which 

15.  16-  were  attached  to  the  sides 

of  the  beaker,  while  those 
which  grew  more  in  the 
interior  had  an  entirely 
different  habit.  The 

crystals  of  the  first  type  averaged  about  2  mm.  in  greatest 
diameter  and  had  the  habit  shown  in  Figs.  15  and  16.  The 
forms  and  angles  are  as  follows : 

a,  100,  i-1  m,  110,  /  e,  101,  1-*  d,  021,  2-i 

b,  010,  i-i  n,  130,  i-3         /,  201,  2-i  p,  111,  1 

Measured.  Calculated.  Measured.    Calculated. 

m  A  ro,  110  A  HO  =    *60°    0'        ...  a  A  p,  100  A  111  =  56°  45'      66°  45$' 

d  A  d,  021  A  021  =  *101°  27f      ...  m  A  />,  110  A  111  -  71°  33$'    71°  33' 

PAp,  111  A  111  =     66°  28$'  66°  29'  p  A  d,  111  A  021  =  36°  54'      36°  54' 

PAp,  111  A  111  =     36°  54'  36°  54'  a  A  e,  100  A  101  =  54°  42$'    54°  42' 

m  A  p,  110  A  111=     60°  43$'  50°43f  a  A/,  100  A  201  =  35°  13'      86°  13$' 

The  crystals  were  brilliant  and  gave  wonderful  reflections. 
The  prismatic  angle  was  measured  repeatedly  and  found  to  be 
60°,  and  the  forms  could  be  referred  to  the  hexagonal  system, 
making  the  m  and  b  faces  a  prism  of  the  first  order,  a  and  n  a 
prism  of  the  second  order,  and  p  and  d  the  unit  pyramid. 
There  was  nothing,  however,  in  the  development  of  the  faces 
to  suggest  hexagonal  symmetry.  Thin  sections  were  pre- 
pared, hoping  that  the  optical  properties  would  throw  some 
light  upon  the  form,  but  they  showed  only  a  very  weak  double 
refraction,  in  fact  they  appeared  almost  like  isotropic  sections, 
so  that  no  satisfactory  conclusions  could  be  drawn. 

The  crystals  of  the  second  type  were  spearhead-shaped, 
Fig.  17,  and  grew  out  into  the  centre  of  the  solution,  either 
attached  to  one  another  by  the  acute  solid  angles,  or  to  a 
slender,  parallel  growth  of  crystals,  which  served  as  a  sort  of 
stem.  The  crystals  which  are  about  5  mm.  in  length  are  com- 
plicated and  perplexing,  and  the  faces  are  developed  with  tri- 


CAESIUM-MERCURIC  HALIDES. 


243 


clinic  symmetry,  although  they  can  be  referred  to  the  axes  of 
the  first  type.  The  most  prominent  faces  are  shown  in  the 
figure,  while  the  distribution  of  all  those  which  gave  distinct 
reflections  are  given  in  the  spherical  projection,  Fig.  18.  The 
forms  which  were  observed  are  given  as  if  they  belonged  to  a 
triclinic  crystal  and  are : 


Fig.  17. 

b,  010,  i-i 
m',  1TO, '/ 
/,  201,  '2-? 
d,  021,  2-T 


Fig.  18. 

JP,  HI,  1' 
/,  Til,  ,1 

?",  ni,  i, 

2, 132,  f-S 


Fig.  19. 


Fig.  20. 


r"',  132,      'f-3  yw,    7f5,'|-f 

/,  T31,       ,3-3  z",    T^7,  f  9' 

w,  T91,       ,9-9  v,  1131,  11-V-' 
af,  T151,  ,15-15 


The  crystals  gave  excellent  reflections,  and  only  occasionally 
a  slight  striation  interfered  with  making  accurate  measure- 
ments. All  of  the  forms  were  observed  on  two  crystals,  and 
probably  others  could  have  been  found  by  measuring  a  larger 
number. 

The  crystals  of  CsHgClBr2  have  a  similar  habit,  Fig.  19, 
and  the  distribution  of  all  of  the  faces  which  gave  distinct  re- 
flections is  given  in  the  spherical  projection,  Fig.  20.  This 
salt  is  more  insoluble  than  the  chloride,  and  the  crystals  are 
consequently  much  smaller,  not  over  1  J  mm.  in  greatest  diam- 
eter. All  of  the  forms  given  above  for  the  chloride  were 
observed  except  z  and  v,  and  in  addition  : 

d',  051,  '2-r  /",  1T1,  '1    /',  T31,  3-3,    u',  T71,  7-7    t,  2T27,  'y-6 


The  crystals  gave  very  good  reflections,  considering  their 
size,  and  the  best  measurements  agreed  so  well  with  those  of 


244  CRYSTALLOGRAPHY  OF  THE 

the  cliloride  that  no  attempt  was  made  to  calculate  a  new  axial 
ratio.  The  most  marked  difference  in  the  two  salts  is  the 
development  of  the  zone  p"  z"  q'"  y'"  in  the  chloride  and  rn 
d'  t'"  qf"  p"ff'w  the  chlorobromide. 

The  measured  and  calculated  angles  are  as  follows : 

CsHgCl3.  CsHgClBr2.  Calculated. 

m'  A  /,     1TO  A  201  44°  45'  45°    6'  44° 

/    A  p,     201  A  111  26°  35'  26°  27'  26° 

p    A  q,     111  A  132  18°  27'  18°  34'  18°  27' 

q    A  d,     132  A  021  18°  26'  18°  23'  18°  27' 

d    A  r,     021  A  T31  26°  44'  26°  26'  26°  34J' 

x     A  r,  T151  A  T31  33°  40'  33°  20'  33°  40^' 

v   A  r,     T91  A  T31  26°  36£'  26°  27'  26°  33' 

u    A  r,     171  A  T31                 ...  21°  35'  21°  47$' 

r     A  /,    T31  A  Til  26°  33'  26°  37'  26°  34^' 

p'  A  /',  Til  A  TT1  36°  52$'  36°  37'  36°  54' 

b     A  r",    OTO  A  151  44°  44'                 ...  44°  58' 

ym  A  ?'",  7S5  A  132  22°  13'                 ...  22°  13' 

z"  A  /',  T37  A  TT1  28°  38'                ...  28°  35' 

q'"  A  p",  132  A  TT1  50°  54'                ...  50°  49' 

y"'  A  q,     735  A  132  62°  29^'  62°  22'  62°  28£' 

.p"  A  v,     III  A  TT3T  60°  46'  ...  60°  45' 

/  A  v,     T11ATT3T  66°  53'  .  .  .  66°  59' 

/    A  /",  201  A  1T1                ...  26°  38'  26°  34$' 

/"A  q'",  ITlA  132                 ...  18°  23'  18°  27' 

q'"  A  £,    132  A  021                ...  18°  34'  18°  27' 

t'"  A  d',  2T27  A  021                ...  10°  13'  10°  19' 

q     A  w,    132  A  T91  50°  59'  51°    4'  50°  46' 

q     A  /",  132  A  1T1                ...  50°  50'  50°  49' 

q    A  ?'",  132  A  132  60°    3'                ...  60°    4' 

It  will  be  seen  from  the  spherical  projection  that  the  forms 
of  CsHgClBr2  lie  mostly  in  three  zones,  suggestive  of  hexag- 
onal rhombohedral  symmetry,  although  there  is  nothing  in 
the  arrangement  of  the  faces,  and  still  less  with  CsHgCls,  to 
indicate  that  this  is  correct.  The  crystals  of  CsHgClBr2  have 
a  slightly  stronger  action  on  polarized  light  than  those  of 
CsHgClg.  When  lying  on  the  large  q  faces,  both  show  an 
extinction  parallel  to  the  edges  between  p,  q  and  d. 


CESIUM-MERCURIC  HALIDES. 


245 


On  a  crystal  of  CsIIgCl3  the  faces  in  the  zone  p,  q,  d,  r 
made  prisms,  which  served  for  the  determination  of  the  follow- 
ing indices  of  refraction: 

Prism  of  36°  54',    021  A  III,    n,  y,  Na  flame  =:  1.791     n,  r,  Li  flame  =  1.779 
Prism  of  63°  28^,  131  A  111,    n,  y,      "      "     =1.792    n,  r,    "      "      =1.779 

The  crystal  was  of  course  very  small  and  the  refracted  rays 
were  not  very  bright,  but  the  latter  were  well  defined  and  the 
double  refraction  was  not  strong  enough  to  separate  them  into 
two  distinct  rays. 

The  author  cannot  give  any  satisfactory  explanation  of 
these  curious  forms.  They  seem  to  illustrate  a  tetartohedral 
development  of  the  faces  of  an  orthorhombic  crystal,  resulting 
in  a  figure  with  triclinic  symmetry.  The  mathematical  rela- 
tions have  been  very  carefully  determined  and  the  facts  given. 
It  is  hoped  that  a  further  study  will  throw  some  light  on  the 
subject. 

The  different  crops  of  CsHgBr3  which  were  examined 
showed  a  variety  of  habits,  represented  by  Figs.  21,  22,  and  23. 


2L 


22. 


23. 


The  forms  and  angles  are  as  follows : 


c,  001,  0 
,  110,  / 


e,  201,  —  2-1 
d,  T01,      \-l 

Measured.     Calculated. 


o,  Til, 
p,  221, 


1  ?/,  261,  —  6-3 

2  x,  T31,      3-3 

Measured.  Calculated. 


c  A  d,  001  A  101  =  *35°  6^ 

c  A  e,  001  A  201  =  52°  28J'   52°  30£ 

c  A  o,  001  A  111  =  45°  40;   45°  49' 


m  Am, 

d  A  x,  101  A  131  =  60°  41'  60°  40' 

e  A  p,  201  A  221  =  38°  46'  38°  46  \' 

e  A  y,  201  A  261  =  67°  21'  67°  28' 


The  crystals  are  seldom  over  5  mm.  in  diameter  and  some- 
times have  a  hemimorphic  development,  although  this  is  not 


246 


CRYSTALLOGRAPHY  OF  THE 


always  apparent.     In  the  prevailing  type,  Fig.  22,  there  is 
perhaps  a  tendency  for  221  to  predominate  over  221,  but  this 
is  not  great.     The  pyramids  x  and  y  were 
24-  observed  only  with  hemimorphic  develop- 

ment, Fig.  23.  The  crystals  were  tested 
for  pyro-electricity,  but  no  satisfactory  re- 
sults were  obtained,  which  is  perhaps 
owing  to  their  small  size.  The  crystals  of  CsHgBrI2  were 
about  2  mm.  in  diameter  and  had  the  habit  shown  in  Fig.  24, 
which  is  quite  different  from  that  of  the  bromide.  The  forms 
and  angles  are  as  follows : 


,  010,  i-i  c,  001,  0  I,  320,  i-f  5,  034,  f  4 

Measured.     Calculated. 

I  A  s,  320  A  034  =  *72°  22'       ... 
I  A  s,  320  A  034  =    76°  16'     76°  50' 


Measured. 

I  A  I,  320  A  320  =  *66°    8' 
b  A  s,  010  A  034  =  *60°  54' 


The  basal  planes  were  curved  and  uneven,  so  that  no  satis- 
factory measurements  could  be  made  from  them,  and  the  other 
faces,  although  bright,  did  not  give  very  satisfactory  reflec- 
tions. The  crystals  show  in  convergent  polarized  light  an 
optical  axis,  almost  normal  to  the  base,  the  plane  of  the 
optical  axes  being  the  clinopinacoid. 


Type  2  :  3. 


Cs2Hg3I8     Monoclinic,  hemihedral 


a     :    b     :     c 
0.3438  :  1  :  0.3544 


=  71°  55J" 


26. 


The  crystals  of  this  salt  have  a  curious  development. 
Some  of  the  most  conspicuous  forms  are  triangular  plates, 
Fig.  25,  while  Fig.  26  is  a  projection  of  the  same  upon  the 


CESIUM-MERCURIC  HALIDES.  247 

clinopinacoid.  These  crystals  are  terminated  above  by  a  basal 
plane  and  below  by  pyramidal  faces,  which  gives  a  curious 
hemimorphic  development  in  the  direction  of  the  symmetry 
plane.  A  variety  of  habits  was  observed,  long  prismatic, 
skeleton  forms  and  simple  shapes  like  Fig.  27,  but  in  almost 
all  of  these  the  hemihedral  character  was  prominent.  The 
crystals  frequently  measured  over  10  mm.  in  greatest  diameter. 
The  faces  were  bright  and  gave  excellent  reflections.  The 
forms  and  angles  are  as  follows  : 

b,  010,  i-i  c,  001,  0  m,  110,  /  p,  111,  1 

The  pyramid  was  observed  only  with  hemihedral  develop- 
ment. 

Measured.  Measured.    Calculated. 

CAW,  001  A  110  =  *72°  51'    m  *p,  110  A  11T  =  *50°  26'       ... 
m  A  m,  110  A  1TO  =  *36°  12'     b  A  p,  010  A  111  =    74°  17'    74°  14' 

Two  cleavages  were  observed,  one  perfect  parallel  to  the 
clinopinacoid,  a  second  less  perfect  parallel  to  the  base.  In 
polarized  light  clinopinacoid  tables  give  an  extinction,  inclined 
about  23°  to  the  vertical  axis  in  the  acute  angle  0.  Basal 
plates  show  in  convergent  light  an  optical  axis  not  far  removed 
from  the  centre  of  the  field.  The  plane  of  the  optical  axes  is 
the  clinopinacoid. 

These  crystals  furnish  an  excellent  illustration  of  inclined 
faced  hemihedrism,  as  recently  developed  by  Prof.  Geo.  H. 
Williams,*  who  has  shown  that  it  is  of  frequent  occurrence 

on  pyroxene. 

Type  1  :  2. 

>,     :     b     :     c 

B  =  78°  64' 


a     :     b     :     c 

CsHg2Cl6 

Monoclinic 

1.6099  :  1  :  1.3289 

CsHg2ClBr4 

Orthorhombic 

0.586    :  1  :    ... 

CsHg2Br6 

Orthorhombic 

0.590    :  1:1.15 

CsHg2I6 

Not  measured. 

s   was 
made  in  slender      / 


lath-shaped  crys-     * *  28 

tals,  over  10  mm. 


*  Amer.  Jour.  Sci.,  xxxviii,  115, 1889. 


248 


CRYSTALLOGRAPHY  OF  THE 


long  in  the  direction  of  the  symmetry  axis,  but  not  over  J  mm. 
in  diameter.  Fig.  28  represents  a  simple,  and  29  a  twin 
crystal,  with  the  orthopinacoid  as  twinning  plane.  The  forms 
and  angles  are  as  follows : 


a,  100,  i-l 

b,  010,  i-i 


c,  001.  0 
m,  110,  I 


d,  Oil,  14 


Two  orthodomes  were  also  identified,  101  and  201,  but  they 
were  very  small  and  yielded  only  approximate  measurements. 


Measured. 

a  A  c,  100  A  001  =  *78°  54'  CAW,  001  A 
a  A  m,  100  A  110  =  *57°  40'  m  A  p,  110  A  111  =  31°  12' 
6-  A  d,  001  A  Oil  =  *52°  31'  a  A  p,  100  A  111  =  58°  4' 

b  A  p,  010  A  111  =  47°  19' 


Measured.     Calculated. 

=  84°  5'  84°  5' 
31°  8' 
58°  3' 
47°  19' 


The  plane  of  the  optical  axes  is  at  right  angles  to  the  sym- 
metry plane,  and  the  obtuse  bisectrix  is  nearly  nor- 
mal to  the  base. 

Both  CsHg2ClBr4  and  CsHg2Br5  were  made  in 
rectangular  tablets,  Fig.  30,  which  were  not  over 
1J  mm.  in  greatest  diameter  and  were  veiy  thin. 
Twins  were  common,  with  the  unit  prism  as  twin- 
ning plane,  and  the  plates  often  penetrated  at  angles 
of  about  60°  and  120°,  reminding  one  of  little 
cerussite  twins. 

The  forms  and  angles  are  as  follows : 


CsHg2ClBr4. 

b,  010,  i-i 

,  110,  / 

d,  Oil,  1-t 


CsHg2Br5. 

b,  010,  Vt 
n,  120,  i-2 

d,  Oil,  i-i 

e,  014,  J-T 


Measured.  Calculated.  Measured.  Calculated. 

m  Am,  110  A  110  =  *eO°  44'      ...          b  A  6,      twin      =  *61°    5'       ... 
b  A  b,      twin      =   60°  35'    60°  44'       6  A  rf,  010  A  Oil  =  *41°   0'      ... 

6  A  n,  010  A  120  =    40°  20'  40°  17' 

b  A  e,  010  A  014  =  *73°  25'  73°  57' 


CESIUM-MERCURIC  HALIDES. 


249 


31. 


Type  1:5. 

a    :     b     :     c 

CsHg5Cln         Monoclinic  0.7233  :  1  :  0.4675       0  =  85°  51'  40" 
CsIig5ClBr10    Monoclinic  0.7111  : 1  :  0.4561       )8  =  85°  29' 

The  chloride  was  made  in  prismatic  crystals, 
fully  10  mm.  long,  and  having  the  habit  shown  in 
Fig.  31.  The  forms  and  angles  are  as  follows : 

m,  110,  /        d,  Oil,  14         e,  TOl,  1-e        /,  101,  -  1-1 
The  dome  /  was  usually  wanting. 

Measured.  Calculated.  Measured.  Calculated, 

m  A  m,  110  A  110  =  *71°  37'       ...  m  A  d,  110  A  Oil  =  72°  31'    72°  31£' 

d  A  d,  Oil  A  Oil  =  *50°    0'       ...  m  A  d,  110  A  Oil  =  78°  49'    78°  48' 

m  A  e,  110  A  101  =  *66°    8'       ...  d  A  /,  Oil  A  101  =  39°  30'    39°  29|' 

d  A  e,  Oil  A  TOl  =    41°  21'  41°  20£'  e  A  /,  101  A  101  =  65°  43'    65°  42' 

The  chlorobromide  CsHg5ClBri0  is  much 
more  insoluble  than  the  chloride  and  was 
made  in   crystals,   which   were   not   over 
£  mm.  in  greatest  diameter.     The  habit  is 
shown  in  Fig.  32,  and  is  very  different 
from  that  of  the  chloride.     The  forms  and  angles  are  as 
follows : 

m,  110,  /  d,  Oil,  14  e,  TOl,  l-i 

Measured.  Measured.  Calculated. 

m  A  m,  110  A  1TO  =  *70°  40'    d  A  «,  Oil  A  101  =  *40°  58'     ... 
d  A  d,  Oil  A  OT1  =  *48°  54'    m  A  d,  110  A  Oil  =    72°  40'  72°  40' 

The  crystals  are  strongly  double  refracting,  and  the  little 
tables  show  in  convergent  polarized  light  a  bisectrix  nearly 
normal  to  e.  The  plane  of  the  optical  axes  is  the  clinopina- 
coid  and  the  optical  axial  angle  is  small.  The  inference  phe- 
nomena are  very  interesting  when  observed  through  colored 
glasses.  In  the  hyperbola  position  the  figure  is  almost  uni- 
axial  when  viewed  through  red  glass,  while  with  blue  the 
hyperbolae  are  separated,  probably  as  much  as  15°-20°. 


SHEFFIELD  SCIENTIFIC  SCHOOL, 
June,  1891. 


ON  THE  CESIUM-  AND  THE    POTASSIUM-LEAD 

HALIDES* 

BY  H.  L.  WELLS. 

As  a  continuation  of  the  work  on  double  halides,  in  this 
laboratory,!  a  study  of  the  caesium-lead  salts  has  been  under- 
taken by  Messrs.  G.  F.  Campbell,  P.  T.  Walden,  and  A.  P. 
Wheeler.  These  gentlemen  have  carried  out  the  investigation 
with  much  enthusiasm  and  skill,  and  I  take  pleasure  in  ex- 
pressing my  obligations  to  them.  They  have  established  the 
following  salts  : 

Cs4PbCl6  Cs4PbBr6 

CsPbCl3  CsPbBr8t  CsPbI8 

CsPb2Cl6  CsPb2Br5 

These  results  showed  the  existence  of  three  types  of  lead 
double  halides,  the  first  of  which  fails  to  conform  with  Rem- 
sen's  law  §  concerning  the  composition  of  this  class  of  bodies. 

Since  the  recent  investigations  of  Remsen  and  Herty  ||  had 
indicated  the  existence  of  only  a  single  type  of  potassium-lead 
halides,  a  new  investigation  of  these  seemed  desirable,  espe- 
cially since  these  authors  had  denied  the  existence  of  Boullay's 
salt,  If  K4PbI6,  which  corresponds  to  one  type  of  the  new 
caesium  compounds.  I  have,  therefore,  undertaken  this  work, 
and,  as  a  result,  have  obtained  the  following  salts  : 

.......  K2PbBr4.H20  ....... 

3KPbCl8.H20  :LBr..H,  KPbI8,2H80 


KPb2Cl6  KPb2Br6 


*  Amer.  Jour.  Sci.,  xlv,  February,  1893. 
t  Ibid.,  Ill,  xliv,  155,  157,  and  221. 
$  This  compound  is  dimorphous. 

§  Amer.  Chem.  Jour.,  xi,  296.  ||  Ibid.,  xiv,  107. 

,  T  Ann.  Chim.  Phys.,  II,  xxxiv,  336  (1827). 


CAESIUM-  AND  POTASSIUM-LEAD  HAL1DES.       251 

It  is  to  be  noticed  that  neither  Boullay's  iodide  nor  any 
corresponding  chloride  or  bromide  was  obtained  among  these 
salts.  On  the  other  hand,  the  compound  K2PbBr4.H2O  be- 
longs to  a  type  which  had  not  been  discovered  among  the 
caesium  salts,  so  that,  taking  the  caesium  and  potassium  series 
together,  the  existence  of  four  types  of  double  lead  halides  is 
shown. 

The  compound  K2PbBr4,  the  anhydrous  form  of  the  salt 
just  mentioned,  is  ascribed  to  Lb'wig,*  but  although  iodides 
belonging  to  the  same  type  have  been  described,  K2PbI4.4H2O 
by  Ditte  f  and  K2PbI4.2H2O  by  Berthelot,  J  neither  Remsen 
and  Herty  nor  I  have  been  able  to  prepare  them.  Although 
these  iodides  and  Boullay's  salt,  K4PbI6,  belong  to  types  which 
certainly  exist,  I  am  inclined  to  believe,  with  Remsen  and 
Herty,  that  the  products  which  gave  these  formulae  were  mix- 
tures of  KPbI8.2H2O  and  KL  The  absence  of  more  than  one 
iodide  in  the  caesium  series  strengthens  this  view. 

Remsen  and  Herty  obtained  the  salt  KPbI8.2H2O  under 
wide  variations  of  conditions,  and  I  have  confirmed  their 
results.  This  salt  was  first  obtained  by  Boullay  §  and  -ana- 
lyzed by  him,  after  drying  over  lime,  in  an  anhydrous  condi- 
tion. Berthelot  ||  has  described  a  compound,  K4Pb3I10.6H2O, 
which  differs  but  slightly  in  required  composition  from  the 
above  salt,  and  his  description  of  it  agrees  with  that  com- 
pound. There  is  no  doubt,  therefore,  that  he  really  obtained 
the  compound  KPbI8.2H2O  and  that  his  analyzed  products 
were  slightly  contaminated  with  potassium  iodide.  Berthelot 
attributes  K4Pb3I10  to  Boullay.  The  latter  chemist,  however, 
derived  the  correct  formula,  equivalent  to  KPbI8,  from  his 
analysis,  but  since  this  did  not  agree  closely  with  theory, 
Gmelin^f  derived  the  above-mentioned  formula  from  it,  and 
this  has  been  frequently  copied  in  more  recent  chemical 
literature. 

*  Gmelin's  Handbook,  English  ed.  of  1850,  v.  162. 
t  Ann.  Chim.  Phys.,  V,  xxiv,  226,  1881.        J  Ibid.,  xxix,  289, 1883. 
§  Ibid.,  II,  xxxiv,  336, 1827.  ||  Ibid.,  V,  xxix,  289, 1883. 

T  Handbook,  English  ed.,  1850,  v,  161. 


252  ON  THE   CsESIUM-  AND   THE 

Schreinemakers,*  in  connection  with  an  investigation  on 
the  equilibrium  of  the  double  salt  of  iodide  of  lead  and  potas- 
sium in  aqueous  solution,  has  assumed  that  Ditte's  formula 
was  correct  as  far  as  the  composition  of  the  anhydrous  compound 
was  concerned.  By  making  a  number  of  water  determina- 
tions, without  determining  lead,  potassium,  or  iodine,  he 
arrived  at  the  formula  K2PbI4.2iH2O.  It  is  absolutely  cer- 
tain, from  his  description  of  the  salt  and  his  method  of  pre- 
paring it,  that  he  had  the  compound  KPbI3.2H2O  ;  moreover, 
his  water  determinations,  5.52,  5.72,  5.89,  5.93,  and  5.16  per 
cent,  agree  satisfactorily  with  the  calculated  amount,  5.90,  for 
this  salt. 

Remsen  and  Herty  made  only  a  single  chloride,  and  likewise 
only  one  bromide.  The  other  chloride,  and  the  two  bromides 
belonging  to  other  types  crystallize  beautifully  and  are  as 
easily  made  as  the  salts  which  they  prepared,  and  it  is  a  strange 
coincidence  that  the  latter  happened  to  correspond  in  type  to 
the  iodide  which  they  had  obtained.  I  have  confirmed  the 
composition  of  their  bromide,  KPbBr3.H2O,  but  their  chloride, 
to  which  they  gave  the  formula  KPbCl2  is  evidently  identi- 
cal with  the  compound  which  I  have  found  to  be  undoubtedly 
hydrous,  3KPbCl8.H2O. 

Lowig,  as  already  mentioned,  has  described  the  compound 
K2PbBr4.  I  have  been  unable  to  find  his  original  article,  but 
from  the  fact  that  I  have  not  obtained  an  anhydrous  form  of 
this  compound,  I  believe  that  he  overlooked  the  water  of 
crystallization  or  dehydrated  the  salt  before  analyzing  it. 

A  bromide,  K2Pb3Br8  is  mentioned  by  Berthelot.f  He  does 
not  give  any  analysis  or  description  of  it,  and  I  am  convinced 
from  my  own  experiments  that  he  obtained  a  mixture  of 
KPbBrs4H2O  and  KPb2Br6. 

Strohecker  f  states  that  he  produced  three  different  chlorides 
of  potassium  and  lead  by  mixing  potassium  chloride  and  lead 
nitrate  solutions.  It  is  remarkable,  considering  the  abundance 

*  Zeitschr.  Physikal.  Chem.,  ix,  57, 1892. 
t  Ann.  China.  Phys.,  V,  xxix,  289,  1883. 
t  Jahresbericht,  1869,  282. 


POTASSIUM-LEAD  HALIDES.  253 

and  cheapness  of  the  materials  and  the  ease  with  which  large 
quantities  of  the  double  salts  can  be  made,  that  he  did  not 
obtain  them  in  sufficient  quantities  for  exact  analyses.  Since 
I  have  succeeded  in  making  only  two  double  chlorides,  I  believe 
that  one  of  Strohecker's  salts,  which  he  describes  as  feathery, 
was  simply  lead  chloride. 

The  results  of  previous  investigators  may  be  summed  up 
by  saying  that  it  is  probable  that  no  potassium-lead  halides  have 
been  correctly  described,  if  water  of  crystallization  is  taken 
into  consideration,  except  two  of  Remsen  and  Herty's  salts, 
KPbBr3.H2O  and  KPbI3.3H2O. 

Method  of  Preparation. 

Both  the  caesium  and  potassium  salts  have  been  investi- 
gated, in  every  case,  by  making  hot,  aqueous  solutions  of  the 
component  halides  and  cooling  to  crystallization.  Some  pre- 
vious investigators  had  used  solutions  of  lead  nitrate  and  an 
alkaline  halide  for  the  purpose,  but  their  example  has  not  been 
followed,  because  it  was  not  believed  that  the  presence  of  an 
alkaline  nitrate  would  in  any  way  facilitate  the  operation,  and 
it  was  feared  that  it  might  incur  contamination  in  some  cases. 
The  conditions  were  gradually  varied  from  a  point  where  the 
alkaline  halide  crystallized  out,  to  a  point  where  the  lead 
halide  was  deposited  uncombined,  and  the  experiments  were 
so  carefully  earned  out  and  so  frequently  repeated  that  it 
seems  scarcely  possible  that  any  double  salt  was  overlooked. 

The  salts  have  been  made  on  a  rather  large  scale.  In  the 
case  of  the  caesium  compounds,  the  rarity  of  the  material  made 
it  necessary  to  perform  the  separate  experiments  with  only 
about  50  or  75  g.  of  a  caesium  halide,  but  in  making  the 
potassium  salts  400  or  500  g.  of  a  potassium  halide  were 
frequently  used. 

Solutions  which  were  neutral  or  slightly  acid  were  generally 
used.  The  effect  of  the  presence  of  a  large  amount  of  free 
acid,  hydrochloric,  hydrobromic,  or  hydroiodic,  as  the  case  re- 
quired, was  also  carefully  studied,  but  these  had  no  apparent 
effect  upon  the  results. 


254  ON  THE  CESIUM-  AND   THE 

Very  large  crops  of  the  potassium  salts  were  sometimes 
formed,  so  that  the  homogeneity  of  the  mass  was  doubtful. 
In  such  cases  the  greater  part  of  the  crop  was  removed  and 
satisfactory  crystals  were  obtained  by  dissolving  the  remainder 
in  the  mother-liquor  by  the  aid  of  heat  and  cooling. 

The  caesium  material  used  was  wholly  from  the  pollucite  of 
Hebron,  Maine.*  The  salts  were  carefully  purified  for  this 
investigation.  Godeffroy's  method  f  was  found  to  be  very 
satisfactory  for  the  purpose  of  separating  caesium  from  the 
sodium  and  potassium  which  accompany  it  in  the  mineral. 

Kahlbaum's  potassium  chloride,  bromide,  and  iodide  were 
usually  used  for  making  the  potassium  salts,  but  for  a  few 
experiments  the  ordinary  medicinal  potassium  bromide  was 
substituted.  Since  some  of  the  analyses  of  the  double  bro- 
mide show  an  excess  over  100  per  cent,  it  is  suspected  that 
the  salts  contained  a  little  chlorine.  Calculation  shows  that 
one  per  cent  of  chlorine  replacing  bromine  would  cause  an 
excess  of  0.71  per  cent  if  the  chlorine  was  weighed  as  silver 
chloride  and  calculated  as  bromine. 

The  lead  halides  which  were  used  were  prepared  by  our- 
selves from  reliable  materials. 

General  Properties. 

The  lead  double  halides  are  all  decomposed  by  water,  and 
the  presence  of  a  large  excess  of  the  alkaline  halide  is  neces- 
sary for  the  formation  of  all  the  compounds  to  be  described 
except  CsPbjjCls  and  CsPb2Br6,  which  are  almost  stable  with 
water.  The  concentration  of  the  alkaline  halide  solution 
evidently  determines,  in  the  cases  of  the  chlorides  and  bro- 
mides, the  type  of  salt  produced.  Since  the  simple  caesium 
halides  are  much  more  soluble  than  those  of  potassium,  it  is 
possible  to  use  them  in  much  more  concentrated  solutions, 
and  the  salts  of  Cs.PbCle  and  Cs4PbBr6  are  readily  obtained. 
In  the  case  of  potassium  bromide  the  solution  becomes  satu- 
rated with  the  simple  salt  by  concentration  just  beyond  the 

*  Amer.  Jour.  Sci.,  Ill,  xli,  213.        f  Berichte  d.  Chem.  Ges.,  vii,  375. 


POTASSIUM-LEAD  HALIDES.  255 

point  where  K2PbBr4.H2O  is  obtained,  and  with  potassium 
chloride,  which  is  less  soluble  than  the  bromide,  the  limit  is 
reached  at  the  compound  3KPbCl3.H2O.  The  apparent  exist- 
ence of  only  a  single  double  iodide,  both  with  caesium  and 
potassium,  is  remarkable,  since  caesium  iodide  is  very  soluble 
and  potassium  iodide  is  much  more  soluble  than  the  bromide 
and  chloride. 

On  account  of  their  decomposition  by  water,  no  determina- 
tions of  the  solubility  of  the  double  halides  have  been  made, 
but  it  was  noticed  that  the  caesium  compounds  were  much  less 
soluble  in  the  saline  solutions  than  the  corresponding  potas- 
sium salts.  This  relation  corresponds  with  the  observation  of 
Godeffroy,*  that  while  the  simple  salts  increase  in  solubility 
from  potassium  to  caesium,  the  double  and  complicated  salts 
show  a  decrease  in  this  direction. 

All  the  chlorides  and  bromides  described  in  this  article  are 
colorless,  or  in  one  case  nearly  so  except  two  caesium  salts, 
CsPbCls  and  one  modification  of  CsPbBr8.  The  first  of  these 
is  pale  yellow  and  the  other  bright  orange.  These  colors  are 
very  remarkable  since  the  simple  halides  from  which  they  are 
made  are  all  colorless.  I  have  previously  observed  a  similar 
case,  where  a  colored  double  halide  was  formed  from  two 
colorless  halides,  in  the  compound  CsHgBr8.  f  Both  double 
iodides  are  yellow,  the  hydrous  potassium  salt  being  the  paler 
of  the  two. 

Analytical  Methods. 

Great  care  was  used  in  selecting  homogeneous  material  for 
analysis.  The  crystals  were  dried  as  rapidly  and  thoroughly 
as  possible  by  pressing  them  between  smooth  filter-papers,  and 
where  the  substance  did  not  lose  its  lustre  by  the  operation, 
it  was  then  exposed  to  the  air  for  several  hours. 

Water  was  determined  by  collecting  and  weighing  it  in  a 
calcium-chloride  tube,  the  substance  being  ignited  in  a  com- 
bustion-tube, behind  a  layer  of  dry  sodium  carbonate,  in  a 

*  Berichte  d.  Chem.  Ges.,  ix,  1365.  t  Amer.  Jour.  Sci.,  Ill,  xliv,  227. 


256  ON  THE   CESIUM-  AND   THE 

current  of  dry  air.  The  water  lost  over  sulphuric  acid  or  at 
certain  temperatures  was  determined  by  the  usual  methods. 

Lead  was  determined  in  two  ways.  With  all  the  caesium 
salts  the  substance  was  dissolved  in  hot  water  (an  easy  opera- 
tion with  all  these  salts,  but  impracticable  in  the  case  of  some 
of  the  potassium  compounds),  and  all  except  a  trace  of  lead 
was  precipitated  by  ammonium  carbonate  in  presence  of  am- 
monium hydroxide.  The  precipitate  of  lead  carbonate  was 
removed  by  filtration,  and  the  remaining  trace  of  lead  was  pre- 
cipitated by  passing  hydrogen  sulphide  into  the  alkaline  solu- 
tion. The  lead  sulphide  was  collected  and  ignited  by  itself  in 
a  porcelain  crucible.  The  amount  of  this  was  so  small  that 
it  was  evident  that  no  appreciable  error  would  arise  from  any 
lead  sulphate  that  the  ignited  residue  might  contain,  so  that 
the  main  precipitate  of  lead  carbonate  was  ignited  in  the  same 
crucible  and  the  whole  was  weighed  and  calculated  as  lead 
oxide.  A  different  method  was  selected  for  the  determination 
of  lead  in  the  potassium  compounds,  for  the  reason  that  some 
of  them  could  not  be  readily  dissolved  in  hot  water,  and  it  was 
found  to  be  more  convenient  and  expeditious  than  the  other. 
About  1  g.  of  substance  was  dissolved  in  about  10  c.  c.  nitric 
acid  (sp.  gr.  1.20),  about  2c.c.  concentrated  sulphuric  acid, 
previously  diluted  with  water,  were  then  added,  and  the  nitric 
acid  was  removed  by  evaporation.  After  diluting  with  about 
25  c.  c.  of  water  and  cooling,  the  lead  sulphate  was  collected 
in  a  Gooch  crucible,  washed  with  very  dilute  sulphuric  acid, 
ignited,  and  weighed. 

In  order  to  determine  csesium,  the  alkaline  solution  from 
which  the  lead  had  been  removed  was  concentrated  until  the 
ammonium  carbonate,  hydroxide,  and  sulphide  had  been  nearly 
or  quite  removed,  a  small  excess  of  sulphuric  acid  was  added, 
and,  after  evaporation  and  ignition,  normal  csesium  sulphate 
was  obtained  by  igniting  in  a  current  of  air  containing  am- 
monia, and  this  was  weighed. 

The  nitrates  from  the  lead  sulphate  did  not  contain  an 
appreciable  amount  of  lead.  Normal  potassium  sulphate  was 
obtained  from  these  solutions  by  evaporating,  igniting,  and 
heating  in  an  ammoniacal  atmosphere. 


POTASSIUM-LEAD  HALIDES.  257 

The  halogens  were  determined  as  silver  halides.  Where 
the  substance  could  be  completely  dissolved  in  hot  water,  an 
excess  of  silver  nitrate  was  added  to  the  hot  solution  and  it 
was  afterwards  acidified  with  nitric  acid.  When  it  happened 
that  the  lead  halide  remained  partly  undissolved,  the  nitric 
acid  was  not  added  until  this  had  been  completely  decomposed 
by  long  digestion  on  the  water-bath  with  an  excess  of  silver 
nitrate.  The  precipitates  were  collected  and  weighed  in  Gooch 
crucibles. 

THE  CAESIUM-LEAD  CHLORIDES. 

BY  G.  F.  CAMPBELL. 

CstPb  C16.  —  When  lead  chloride  is  dissolved,  by  the  aid  of 
heat,  in  a  solution  of  caesium  chloride  which  is  so  concentrated 
as  to  be  nearly  saturated  when  cold,  this  salt  is  deposited  on 
cooling  in  the  form  of  brilliant  white  rhombohedrons.  Crys- 
tals having  a  diameter  of  2  or  3  mm.  were  sometimes  obtained. 
Two  entirely  separate  crops  were  analyzed,  both  of  which  were 
undoubtedly  free  from  other  compounds. 


For 

Caesium    ....    55.60 
Lead   

md. 

56.03 
21.63 
22.23 

Calculated  for 

C84PbCl«. 

55.90 
21.75 
22.35 

Chlorine  ....    21.97 

99.89 

100.00 

CsPl  Cls.  —  On  gradually  diluting  the  concentrated  solution 
of  csesium  chloride,  such  as  was  used  in  making  the  previous 
salt,  and  dissolving  lead  chloride  in  it  as  before,  a  point  is  soon 
reached  where  short  prismatic  crystals  of  small  size  and  of  a 
pale  yellow  color  are  deposited  on  cooling.  Three  different 
crops  of  apparently  pure  crystals  were  analyzed. 


Caesium 

Lead 

Chlorine 


Pound. 

Calculated  for 
CsPbCls. 

29.79 

31.33 

30.54 

30.13 

44.99 

45.28 

46.29 

46.36 

23.85 

23.75 

23.71 

23.85 

100.17 

99.57 

100.13 

100.00 

17 


258 


ON  THE   CESIUM-  AND   THE 


^  01B.  —  Experiments  with  still  more  dilute  solutions, 
carried  out  in  a  similar  manner,  gave,  under  wide  variations 
of  conditions,  this  salt  in  the  form  of  thin  white  plates  which 
were  often  several  millimeters  in  diameter.  These  plates  pre- 
sented marked  variations  in  habit,  which  were  apparently  due 
to  changes  in  the  conditions  under  which  they  were  made. 
In  two  crops,  of  which  A  and  B  are  the  analyses,  the  plates 
were  uniformly  rhomboidal  in  form.  Two  other  crops,  C  and 
D,  were  made  up  of  lengthened  plates,  so  twinned  as  to  form 
feathery  aggregates.  In  another  crop,  E,  made  from  a  more 
dilute  solution  than  the  others,  the  plates  were  apparently 
square. 


Caesium 

Lead 

Chlorine 


Calculated  for 
CsPb,Cl5. 

18.36 

19.99 

B. 

18.44 

c. 
18.27 

D. 

E. 

18.45 

57.14 

57.16 

57.06 

56.98 

57.08 

57.16 

.  .  . 

24.47 

.  ,  . 

24.52 

24.35 

24.48 

100.07 


99.88      100.00 


The  three  different  habits  in  which  this  salt  crystallizes  are 
so  distinct  in  appearance  that,  before  the  samples  were  ana- 
lyzed, it  was  supposed  that  they  were  separate  compounds.  It 
.appears  probable  that  the  compound  is  at  least  dimorphous. 

THE  CAESIUM-LEAD  BROMIDES. 

BY  P.  T.  WALDEN. 

CsiPbBrs.  —  This  salt  is  produced,  in  concentrated  solutions, 
similarly  to  the  corresponding  chloride.  Like  the  latter  salt,  it 
forms  white  rhombohedrons.  The  crystals  were  usually  not 
over  1  or  2  mm.  in  diameter.  Two  separate  crops  were  prepared 
and  analyzed. 

Found. 

Caesium  ....  43.61  43.42 
Lead  ....  16.83  16.83 
Bromine  39.24  39.33 


Calculated  for 
Cs4P'bBr6. 

43.64 
16.98 
39.38 


99.68        99.58 


100.00 


CsPbBrs.  —  This  compound  is  dimorphous.     One  modifica- 
tion forms  small  prisms  of  a  bright  orange  color,  the  other  is 


POTASSIUM-LEAD  HAL1DES.  259 

pure  white  and  crystallizes  in  slender  needles.  The  orange 
salt  is  obtained  when  lead  bromide  is  dissolved  in  somewhat 
more  dilute  solutions  of  caesium  bromide  than  those  required 
for  the  formation  of  Cs4PbBr6,  and  there  is  a  narrow  range  of 
conditions  where  it  crystallizes  upon  the  latter  salt.  There  is, 
therefore,  no  evidence  of  the  existence  of  an  intermediate 
compound,  CsaPbBr4,  corresponding  to  one  of  the  potassium- 
lead  bromides.  Whenever  solid  lead  bromide  is  added  to  a 
concentrated  solution  of  caesium  bromide,  it  instantly  loses  its 
white  color  and  takes  on  that  of  the  orange  salt.  The  white 
needles  are  formed  in  solutions  which  are  slightly  more  dilute 
than  those  required  for  the  orange  modification.  The  limits 
of  the  conditions  under  which  this  white  salt  is  formed  are 
very  narrow,  and  a  great  many  trials  were  necessary  before 
satisfactory  crops  were  obtained.  Two  distinct  samples  of 
each  salt  were  analyzed.  The  white  needles  were  not  abso- 
lutely free  from  the  orange  compound,  but  there  is  no  doubt 
that  they  were  sufficiently  pure  to  show  their  composition 
accurately. 

Caesium  .  .  . 
Lead  .... 
Bromine  .  .  . 

100.25    99.86    99.73    99.82      100.00 

On  heating  the  white  modification  to  about  140°,  it  gradu- 
ally assumes  the  exact  color  of  the  orange  salt,  without  chang- 
ing its  external  form,  and  this  color  is  permanent  on  cooling. 

CsPb2BrB. — This  salt  is  produced  in  solutions  which  are 
still  more  dilute  than  those  from  which  the  preceding  com- 
pounds are  obtained.  It  was  first  noticed  at  a  volume  of 
about  160  c.  c.  of  a  solution  containing  about  50  g.  of  caesium 
bromide.  It  continued  to  form,  on  further  dilution  and  the 
addition  of  lead  bromide,  until  the  volume  reached  1250  c.  c., 
when  lead  bromide  began  to  be  deposited.  The  conditions 
under  which  the  salt  is  formed  are,  therefore,  very  wide.  The 
compound  crystallizes  in  thin  white  plates,  which,  like 


Calculated  for 
CsPbBr3. 

22.93 
35.69 
41.38 

Orange  Salt. 

23.19    23.13 
35.69    35.39 
41.37    41.34 

White  Salt. 

23.02    22.49 
35.24    35.88 
41.47    41.45 

260  ON  THE  CAESIUM-  AND  THE 

the  corresponding  chloride,  present  considerable  differences 
in  habit.  Plates  having  a  diameter  about  5  mm.  were 
sometimes  obtained.  Three  separate  crops  of  crystals  were 
analyzed. 


Pound.  Calculated  for 
* *  CsPb2Br6. 


Osium       .    .    14.13        14.35 
Lead      .     .     .    43.39        43.72        43.45 
Bromine     .     .     42.23        42.21 

99.75  100.28 


THE  CAESIUM-LEAD  IODIDE  AND  SOME  MIXED  DOUBLE 
HALIDES. 

BY  A.  P.  WHEELER. 

CsPlIy  —  Under  a  great  variety  of  conditions  this  was  the 
only  double  iodide  that  could  be  produced.  The  compound  is 
but  slightly  soluble  in  hot  caesium-iodide  solutions,  so  that  the 
crops  obtained  were  always  small.  It  forms  very  slender 
rectangular  prisms  which  are  yellow  in  color.  The  following 
analyses  were  made  on  separate  products : 


Found. 


Calculated  for 


CsPbIs. 

Caesium  ....    17.90  .  .  .  18.45 

Lead       ....    28.38  27.40  28.71 

Iodine     ....    52.83  52.57  52.84 

99.11  100.00 


Three  double  salts  have  been  made  by  dissolving  lead 
bromide  in  solutions  of  caesium  chloride.  The  analyses  show 
that  the  two  salts  do  not  combine  unchanged,  but  that  there 
is  usually  an  extensive  exchange  of  halogens.  Each  of  the 
products  must  be  considered,  therefore,  as  a  mixture  of  a 
double  chloride  with  the  corresponding  double  bromide. 

(7s4P6(  01,  Br)t.  —  This  was  produced  in  rhombohedrons,  like 
the  chloride  and  bromide.  Two  crops  were  analyzed. 


POTASSIUM-LEAD  HALIDES.  261 

Found. 

Caesium 54.65  55.50 

Lead 19.30  18.61 

Chlorine       ....     15.89  19.90 

Bromine       ....      9.52  4.03 

99.36  98.04 

Katio  Br  :  Cl    .     .     .  1  :  3.8  1  :  11.2 

CsPb(  Cl,  £r)3.  —  This  occurred  in  small  rectangular  prisms, 
like  the  chloride  and  bromide  and  having  a  yellow  color  in- 
termediate between  them.  Two  crops  gave  the  following 
analyses : 

Found. 

Caesium 30.24  30.50 

Lead    ......    44.23  43.55 

Chlorine 21.44  18.94 

Bromine 4.00  8.79 

99.91  101.96 

Katio  Br  :  Cl     .     .     .     1  :  12  1  :  4.8 

CsPbz(CI9  Br)i.  —  This  was  obtained  in  white  plates  resem- 
bling the  two  double  salts.  Two  products  were  analyzed. 

Found. 

Caesium 18.94 

Lead 51.40  51.97 

Chlorine 16.29  19.31 

Bromine 13.27  8.62 

99.90 

Eatio  Br  :  Cl                   1  :  2.8  1:5 


THE  POTASSIUM-LEAD  HALIDES. 

In  studying  these  bodies  care  has  been  taken  to  record  the 
conditions  under  which  they  were  made.  These  conditions  in 
many  cases  are  only  approximately  given,  because  uncertain 
quantities  of  salts  had  often  been  removed  from  the  solutions, 
either  for  analysis  or  in  order  to  obtain  smaller  and  better 
crops  of  crystals.  A  large  number  of  analyses  have  been 


262 


ON  THE   CESIUM-  AND   THE 


made  in  some  cases.  This  was  due  to  the  fact  that  the  salts 
often  varied  so  little  in  appearance  that  it  was  necessary  to 
analyze  many  products  in  order  to  identify  them  and  to  be 
certain  that  they  were  not  different  compounds. 

3KPbOls.ffsO.  —  When  lead  chloride  is  dissolved  in  a  hot 
solution  of  potassium  chloride  which  is  so  concentrated  as  to 
be  nearly  saturated  when  cold,  this  double  salt  is  deposited  on 
cooling.  It  forms  brilliant  prismatic  crystals  which  are  largest 
in  the  most  concentrated  potassium-chloride  solutions.  The 
largest  crystals  obtained  had  a  length  of  more  than  10  mm. 
and  a  diameter  of  1  or  2  mm.  It  was  noticed  that,  when  suffi- 
ciently concentrated  solutions  were  used,  pure  potassium 
chloride  crystallized  upon  this  compound,  and  no  evidence 
was  obtained  of  the  existence  of  a  double  salt  containing  a 
larger  proportion  of  potassium  chloride  than  this. 

The  following  table  gives  the  approximate  conditions  under 
which  the  five  samples  which  were  analyzed  were  made : 


A 
B 
C 

D 
E 


The  results  of  the  analyses  are  as  follows : 

Pound. 


KC1. 

PbCl2. 

Volume. 

Volume  for 
1  g.  KCL 

g- 

g- 

c.  c. 

c.  c. 

400 

30 

1100 

2| 

400 

80 

1200 

3 

150 

40 

450 

3 

100 

25 

350 

3£ 

300 

55 

1300 

H 

K  .    . 

A. 

.    11.38 

B. 

11.10 

c. 
10.79 

D. 

E. 

3KPbCl3.H20. 

1090 

Pb      . 

Cl  .    . 

.    57.46 
.    29.91 

57.68 
29.87 

57.43 
29.81 

57.94 

57.14 

57.73 
29.70 

H20    . 

.      1.45 

1.39 

1.51 

1.88 

1.67 

100.20 

100.04 

100.00 

All  the  samples  were  thoroughly  air-dried  before  they  were 
analyzed.  By  this  treatment  the  crystals  did  not  lose  any  of 
their  lustre.  A  finely  pulverized  portion  of  sample  A  lost 
only  0.02  per  cent  in  weight  after  standing  over  concentrated 


POTASSIUM-LEAD  HALIDES.  263 

sulphuric  acid  for  eight  days.  The  same  sample  suffered  an 
additional  loss  of  0.23  per  cent  when  heated  for  twelve  hours 
in  a  steam  drying-oven.  The  water  was  not  rapidly  given  off 
until  a  temperature  of  about  200°  was  reached.  The  salt 
decrepitates  when  heated  rapidly  to  about  200°,  corresponding 
in  this  respect  to  the  salt  which  Remsen  and  Herty  described 
as  anhydrous  and  to  which  they  gave  the  formula  KPbCls. 
There  can  be  no  doubt,  therefore,  that  Remsen  and  Herty's 
formula  is  incorrect. 

KPbz  C15.  —  This  salt  is  formed  in  more  dilute  solutions  than 
those  which  produce  the  previously  described  compound.  It 
occurs,  like  that  compound,  in  white  prismatic  crystals,  but  it 
differs  considerably  from  it  in  lustre  and  form,  so  that  the  two 
salts  can  be  distinguished  by  microscopic  examination.  The 
salt  under  consideration  is  anhydrous,  and  this  fact  makes  it 
easy  to  distinguish  this  compound,  when  pure,  from  the  other. 

Four  analyzed  crops  were  made  under  the  following  condi- 
tions : 

Volume  for 
1  g.  KC1. 

g.  g.  c.  c. 

A 
B 

C 150  20  1100  7£ 

D 

The  analyses  were  as  follows : 

Pound-  Calculated  for 


KC1. 

PbCl,. 

Volume. 

200 

g- 

50 

c.c. 

1500 

150 

30 

1100 

150 

20 

1100 

250 

55 

1200 

Potassium  .  . 
Lead  .... 

A. 

.      6.14 
.     64.74 

B. 

5.97 
66.43 

c. 
6.18 
65.85 

D. 

6.07 
65.72 

KPb2Cl8 

6.20 
65.65 

Chlorine  .  . 
Water  .  .  . 

.    28.11 
.      0.11 

28.13 

28.08 

28.15 
0.00 

99.10  100.16       99.87     100.00 

There  was  no  indication  of  the  formation  of  any  other 
double  chloride,  as  the  dilution  was  increased  beyond  that 
given  for  the  above  products,  and  when  a  solution  containing 
1  g.  of  KC1  in  11  c.  c.  was  used  pure  lead  chloride  was  deposited. 
H^O — This  salt  is  obtained  by  dissolving  lead 


264 


ON  THE   CAESIUM-  AND   THE 


bromide  in  the  most  concentrated  solutions  of  potassium 
bromide.  It  forms  brilliant  prismatic  crystals  which  are 
permanent  in  the  air.  The  largest  of  these  which  were  ob- 
tained were  about  1  mm.  in  diameter  and  5  mm.  in  length.  A 
number  of  crops  were  made  under  the  following  conditions : 


A 
B 
C 

D 
E 
F 


KBr. 
400 

400 
400 
400 
500 
500 


PbBr2 
g- 

70 
90 
120 
130 
130 
130 


Volume, 
c.  c. 

700 
700 
800 
650 

850 

775 


Volume  for 
1  g.  KBr. 

If 
If 

2 


These  products  gave  the  following  analyses : 


A  

K. 

12.51 

Pb. 

34.25 

Br. 

51.47 

H20. 

2.50 

=  100.73 

B  

1221 

34.59 

51.21 

2.51 

-  100.52 

c  

11.89 

34.47 

51.14 

2.44 

=    99.94 

D  

12.37 

34.50 

51.35 

E  

34.26 

51.40 

2.61 

1270 

3389 

51.46 

2.57 

-  100.62 

Calculated  for 
K2PbBr4.H20 

33.21 

51.35 

2.89 

=  100.00 

This  salt  is  apparently  stable  in  the  air,  but  it  loses  water 
very  slowly  over  sulphuric  acid.  A  finely  powdered  sample  of 
A  lost  0.23  per  cent  after  remaining  twelve  hours  in  the  desic- 
cator, and  the  same  portion  suffered  an  additional  loss  0.33 
after  eight  days.  A  sample  which  was  not  pulverized  lost  only 
0.09  per  cent  in  twelve  hours  and,  in  addition,  0.17  per  cent  in 
eight  days.  About  one-half  of  the  water  went  off  when  the 
substance  was  heated  for  twelve  hours  in  a  steam  drying-oven. 
At  200°  the  water  is  rapidly  and  completely  expelled. 

QKPbBrs.Hz  0.  —  The  conditions  under  which  this  salt  can 
be  made  are  rather  narrow,  and  these  conditions  encroach  upon 
those  of  the  preceding  compound,  so  that  small  differences  in 
the  amounts  of  lead  chloride  used  or  in  the  temperature  of 
the  solution  are  sufficient  to  cause  the  formation  of  the  other 


POTASSIUM-LEAD  HALIDES. 


265 


salt.  It  forms  brilliant,  colorless,  lozenge-shaped  crystals 
which  can  be  easily  distinguished  from  the  other  compound. 
The  crystals  which  were  obtained  sometimes  had  a  diameter  of 
2  or  3  mm. 

The  crops  analyzed  were  made  under  the  following  con- 
ditions : 


A 

B 
C 
D 

E 


The  analyses  were  as  follows : 


KBr. 

PbBr,. 

Volume. 

g. 

500 

g- 

130 

c.  c. 

950 

500 

130 

1050 

500 

140 

900 

500 

120 

1050 

500 

120 

1125 

Volume  for 
1  g.  KBr. 


2* 


A  

K. 

,    8.44 

Pb. 

41.91 

Br. 

H20. 

129 

B  .    .    .    .    , 

,    802 

4271 

4895 

1  62  — 

101  30 

C  .    .    .    . 

,     8.60 

41.61 

49.16 

1.60  — 

10097 

D  

,    8.08 

42.69 

48.91 

1  14  — 

10082 

E  

4261 

117 

Calculated  for 
3KPbBr8.H2O 

i  7.95 

42.06 

48.77 

1.22  = 

100.00 

The  salt  is  stable  in  the  air.  A  sample,  after  standing 
seven  days  over  sulphuric  acid,  lost  only  0.04  per  cent.  The 
water  is  given  off  very  slowly  at  100°. 

KPbBrz.H<i  0.  —  This  salt  was  described  by  Remsen  and 
Herty.  At  summer  temperature,  about  25°,  I  was  unable  to 
obtain  it,  but  by  placing  the  mother-liquors  from  the  preced- 
ing salt  in  an  ice-chest,  beautifully  crystallized  crops  of  it 
were  obtained. 

Its  formation  was  also  noticed  at  laboratory  temperatures 
when  the  weather  was  somewhat  cooler  than  in  midsummer. 
It  forms  prismatic  crystals.  Some  of  those  obtained  were 
about  10  mm.  long  and  2  mm.  in  diameter.  Two  crops  were 
analyzed. 


266  ON  THE   CAESIUM-  AND   THE 

„       ,  Calculated  for 

KPbBr3.H20. 

Potassium 8.24  7.90  7.76 

Lead 41.23  41.20  41.06 

Bromine 47.81  .  .  .  47.61 

Water 3.28  3.64  3.57 

100.56  100.00 

The  salt  is  usually  permanent  in  the  air,  but  in  dry  weather 
the  crystals  gradually  become  opaque,  and  over  sulphuric 
acid  about  two-thirds  of  the  water  is  rapidly  given  off. 

KPbzBr5.  —  This  salt  crystallizes  in  square  plates,  sometimes 
3  or  4  mm.  in  diameter.  It  can  be  readily  distinguished  from 
the  other  double  bromides,  not  only  by  its  form,  but  from  the 
fact  that  it  quickly  assumes  a  pale  green  color  when  exposed 
to  daylight.  On  long  exposure,  or  in  direct  sunlight,  this 
color  changes  to  a  pale  dirty-brown.  I  have  observed  that 
lead  bromide  itself  becomes  nearly  black  on  long  exposure  to 
daylight.  This  fact  does  not  appear  to  be  generally  known. 

The  samples  analyzed  were  made  under  the  following 
conditions : 

KBr.  PbBr,.  Volume. 

A 400  130  1050 

B 400  150  1250 

C 200  75  1000 


The  results  of  the  analyses  are  as  follows  : 

Found. 


A. 

B. 

c. 

Potassium    . 

.      4.75 

4.75 

4.71 

Lead  .     .    . 

.     49.22 

49.11 

48.48 

Bromine  .     . 

.    47.03 

46.98 

46.89 

101.00 

100.84 

100.08 

Calculated  for 
KPb2Br8. 

4.58 

48.53 
46.89 


100.00 


.  —  It  has  already  been  mentioned  that  this  is 
the  only  double  iodide  that  either  Remsen  and  Herty  or  I 
have  been  able  to  make.  It  forms  slender,  pale  yellow  needles, 
and  is  produced  under  a  great  variety  of  conditions.  Two 
samples  were  analyzed.  A  was  made  with  about  450  g.  KI, 


POTASSIUM-LEAD  HALIDES.  267 

75  g.  PbI2,  and  600  c.  c.  volume.    For  B  about  400  g.  KI, 
45  g.  PbI2,  and  280  c.  c.  volume  were  used. 

Found.  Calculated  for 

A.                     B.  KPbIs.2H,0. 

Potassium 6.03          6.07  5.90 

Lead 30.73        30.13  31.21 

Iodine 57.57        56.99  57.46 

Water 5.26          6.04  5.43 

99.59        99.23  100.00 

The  salt  is  apparently  stable  in  the  air,  but  it  loses  water  in 
the  desiccator. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
October,  1892. 


ON  THE  DOUBLE  HALIDES  OF  TELLURIUM  WITH 
POTASSIUM,  RUBIDIUM,  AND  CESIUM.* 

BY  H.  L.  WHEELER. 

THE  existence  of  double  halides  of  tellurium  with  potas- 
sium, sodium,  and  ammonium  was  first  indicated  by  Berzelius.f 
He  described  the  methods  by  which  he  obtained  them,  but 
gave  no  analyses  of  the  compounds.  Later,  RammelsbergJ 
investigated  the  double  chlorides  of  tellurium  with  potassium 
and  ammonium,  with  the  object  of  determining  their  composi- 
tion. He  arrived  at  the  formula?  8KC1.3TeCl4  and  8NH4C1. 
3TeCl4.  It  will  be  shown  beyond  that  the  formula  of  the 
potassium  compound  at  least  must  have  been  obtained  from 
analyses  of  impure  products.  Von  Hauer§  analyzed  the 
double  bromide  of  tellurium  and  potassium,  and  concluded 
that  the  salt  had  the  composition  represented  by  the  formula 
2KBr.TeBr4.3H2O.  I  have  reinvestigated  this  salt  and 
found  it  to  contain  two  molecules  of  water  and  not  three. 
Probably  Von  Hauer  analyzed  the  salt  without  previously 
having  dried  it  sufficiently  or  without  haying  taken  precau- 
tions to  remove  included  water  which  the  crystals  always  con- 
tain. He  dehydrated  this  salt  and  used  it  in  his  work  on 
the  atomic  weight  of  tellurium. 

More  recently  Wills  ||  determined  the  atomic  weight  of 
tellurium  by  means  of  the  same  salt.  He  does  not  give  any 
analyses  of  the  hydrous  compound,  but  states  that  the  salt 
contains  water  and  gives  directions  for  dehydrating  it.  Ram- 
melsberg  in  his  "  Handbuch  der  krystallographisch-physi- 
kalischen  Chemie"  (p.  289)  quotes  the  formula  of  the 

*  Amer.  Jour.  Sci.,  xlv,  April,  1893.         t  Pogg.  Ann.,  xxxii,  577. 
t  Berlin  Monats.  Ber.,  1875,  379.  §  J.  prakt.  Chem.,  Ixxiii,  98. 

||  Jour.  Chem.  Soc.,  xxxv,  711. 


DOUBLE  HALIDES  OF  TELLURIUM.  269 

dehydrated  compound  from  Wills's  work  and  assigns  to  this 
Baker's  *  measurements,  which  do  not  belong  to  it,  but  to  the 
hydrated  compound  with  the  three  supposed  molecules  of 
water  of  crystallization.  The  present  investigation  has  shown 
that  the  anhydrous  salt  is  isometric,  the  hydrous  one  being 
orthorhombic. 

Ramsay  f  says  that  "  By  mixing  aqueous  solutions  of 
the  constituent  halides,  tellurium  halides  combine  thus : 
TeCl42KCl,  TeBr4.2KBr,  TeI4.2KI.  These  compounds  form 
reddish  crystals.  Few  attempts  have  been  made  to  prepare 
double  halides."  Although  a  thorough  search  of  the  litera- 
ture on  this  subject  has  been  made,  in  connection  with  the 
present  work,  no  analyses  of  the  double  chloride  or  iodide 
could  be  found.  Berzelius's  work  as  regards  their  prepara- 
tion and  Rammelsberg's  attempt  to  determine  the  formula  of 
the  chloride  comprise  all  the  work  that  has  been  done  on  these 
two  salts.  It  must  be  concluded  that  the  formulae  given  by 
Ramsay  were  deduced  by  analogy  with  the  double  bromide, 
especially  since  his  statements  in  regard  to  color,  method  of 
preparation  and  composition  only  apply,  in  all  respects,  to  the 
double  bromide. 

It  will  be  seen  from  the  above  summary  that  very  little 
satisfactory  work  has  been  done  on  this  class  of  compounds, 
and  therefore  the  present  investigation  has  been  undertaken 
with  the  view  of  making  a  thorough  study  of  the  double 
halides  of  tellurium  with  potassium,  rubidium,  and  csesium. 
As  a  result  the  following  compounds  have  been  prepared : 

2KCl.TeCl4  2RbCl.TeCl4  2CsCl.TeCl4 

2KBr.TeBr4  2RbBr.TeBr4  2CsBr.TeBr4 

2KBr.TeBr4.2H20  2RbI.TeI4  2CsLTeI4 

2KI.TeI4.2H20  

It  is  to  be  noticed  that  all  of  these  compounds  conform  to 
the  usual  type  of  double  halides  of  tetravalent  metals  in  con- 

*  Jour.  Chem.  Soc.,  xxxv,  711. 

t  System  of  Inorganic  Chemistry,  edition  of  1891,  p.  168. 


270         DOUBLE  HALIDES   OF  TELLURIUM  WITH 

taining  the  alkali  metal  and  tellurium  in  the  ratio  of  two 
atoms  of  the  former  to  one  of  the  latter,  and  no  indications  of 
the  formation  of  salts  of  a  different  type  were  observed.  The 
anhydrous  double  halides  of  tellurium  crystallize  in  the  isomet- 
ric system  with  an  octahedral  habit,  and  it  is  an  interesting 
fact  that  this  form  seems  to  be  characteristic  for  anhydrous 
double  halides  of  this  type.  The  caesium  and  rubidium  salts 
are  new  compounds,  as  well  as  the  crystallized,  anhydrous, 
double  potassium  bromide.  New  formulas  have  been  assigned 
to  the  hydrous  potassium  double  bromide  and  to  the  double 
iodide  of  potassium.  A  considerable  difference  is  shown  in 
the  affinity  of  the  double  halides  of  tellurium  and  potassium 
for  water  of  crystallization.  The  double  chloride  is  anhydrous 
and  no  hydrous  form  of  it  was  observed,  the  double  bromide 
was  prepared  in  both  the  hydrous  and  the  anhydrous  forms, 
while  the  iodide  was  obtained  only  with  water  of  crystalliza- 
tion. This  water  was  more  firmly  held  than  in  the  case  of 
the  hydrous  bromide,  as  was  shown  by  the  fact  that  it  formed 
from  hot  solutions  and  did  not  as  readily  effloresce. 

The  methods  used  in  the  preparation  of  pure  material  for 
this  work,  and  which  deserve  to  be  mentioned  on  account  of 
giving  satisfactory  results,  are  given  below.  The  tellurium 
was  obtained  by  purifying  the  commercial  product  by  precipi- 
tation with  sulphurous  acid,  according  to  the  method  of 
Divers  and  Shimose*.*  The  halides  of  tellurium  were  pre- 
pared from  this  material  in  the  usual  way. 

Caesium  chloride  was  obtained  in  a  pure  state  by  the 
method  of  Godeffroy.f  The  bromides  and  iodides  were  ob- 
tained in  the  usual  manner  from  the  carbonate,  the  latter 
having  been  prepared  from  the  pure  chloride  by  converting 
into  nitrate,  then  into  oxalate  and  igniting  the  latter,  as  sug- 
gested by  J.  L.  Smith,J  for  the  conversion  of  potassium 
chloride  into  carbonate.  The  rubidium  was  purified  by 
Allen's  §  acid  tartrate  method.  In  the  case  of  the  potassium 
salts,  Kahlbaum's  pure  material  was  used. 

*  Jour.  Chem.  Soc.,  xlvii,  439.  f  Ber.  d.  chem.  Ges.,  rii,  375. 

t  Amer.  Jour.  Sci.,  II,  xvi,  373.  §  Ibid.,  xxxiv,  367. 


POTASSIUM,   RUBIDIUM,  AND   CAESIUM.  271 

The  methods  by  which  the  double  halides  were  obtained 
will  be  given  with  the  description  of  the  salts. 

Method  of  Analysis. 

The  anhydrous  salts  were  removed  from  the  mother-liquor, 
and,  after  pressing  on  filter  paper,  were  dried  in  the  air.  The 
hydrous  compounds  were  rapidly  crushed  on  smooth  filter 
paper,  and,  as  soon  as  it  was  certain  that  no  included  water 
was  retained  by  the  fragments,  they  were  placed  in  weigh- 
ing tubes.  Portions  of  about  half  a  gram  were  taken  for 
analysis.  In  order  to  determine  the  halogens,  silver  sulphate 
was  added  to  the  solution  of  the  weighed  sample  in  water 
containing  a  little  sulphuric  acid.  The  silver  halide  was 
washed,  ignited,  and  weighed  in  the  usual  manner.  After  the 
removal  of  the  excess  of  silver  by  means  of  hydrochloric  acid, 
tellurium  was  removed  with  hydrogen  sulphide.  This  separa- 
tion of  tellurium,  best  in  warm  solution,  has  been  found  to  be 
complete  in  a  few  minutes  and  in  a  condition  that  admits  of 
filtration  without  inconvenience.  The  sulphide  of  tellurium, 
filtered  on  asbestos  in  a  Gooch  crucible,  was  washed  with 
water  containing  a  little  hydrogen  sulphide,  then  treated  with 
a  solution  of  bromine  in  dilute  hydrochloric  acid,  which 
readily  dissolves  the  moist  sulphide.  An  excess  of  nitric  acid 
was  then  added  to  this  solution  and  the  whole  evaporated  on 
the  water  bath ;  the  resulting  tellurous  acid,  being  transferred 
to  platinum,  was  ignited  and  weighed  as  TeO2.  The  alkali 
metals  were  determined  by  evaporating  the  filtrate  from  the 
tellurium  sulphide  to  dryness,  with  an  excess  of  sulphuric  acid. 
The  residues  were  then  converted  into  normal  sulphate  by 
ignition  in  a  stream  of  ammonia,  as  suggested  by  Kriiss  for 
potassium  sulphate.  In  the  case  of  the  hydrous  salts,  water 
was  determined  by  heating  them  in  an  air  bath  to  constant 
weight ;  the  residues  were  analyzed  and  found  to  correspond 
in  composition  to  the  anhydrous  salts.  The  atomic  weights 
used  in  the  calculation  of  the  results  were  the  following: 

Te,  125 ;  K,  39.1 ;  Eb,  85.5 ;  Cs,  133  ;  01,  35.5  ;  Br,  80 ;  I,  127. 


272         DOUBLE  HALIDES  OF  TELLURIUM  WITH 

Solubility. 

The  salts  are  all  decomposed  by  water.  The  double 
bromides,  however,  show  an  interesting  difference  in  their 
deportment  with  this  reagent.  Potassium  tellurium  bromide 
dissolves  in  a  small  amount  of  water,  but,  if  an  excess  of 
water  is  added,  tellurous  acid  separates,  as  has  been  observed 
by  Wills.*  Rubidium  tellurium  bromide  also  dissolves  in  a 
little  hot  water  completely,  the  difference  being  shown  on 
cooling,  when  a  considerable  portion  of  the  tellurium  sepa- 
rates as  tellurous  acid.  In  the  case  of  the  caesium  salt 
both  hot  and  cold  water,  in  large  and  small  amounts,  fail  to 
dissolve  the  salt,  the  result  being  immediate  decomposition. 
Only  a  small  part  of  the  tellurium  in  this  case  goes  into  solu- 
tion. Most  of  these  double  salts  can  be  conveniently  recrys- 
tallized  from  dilute  solutions  of  the  corresponding  acid.  The 
exceptions  are  potassium-tellurium  chloride,  which  is  decom- 
posed by  this  treatment,  and  caesium-tellurium  iodide,  which 
is  practically  insoluble  in  hydriodic  acid.  The  fact,  first 
noticed  by  Godeffroy,f  that  double  halides,  containing  the 
metals  potassium,  rubidium,  and  caesium,  generally  decrease  in 
solubility  from  potassium  to  caesium,  which  has  frequently 
been  noticed  in  this  laboratory,  is  again  well  illustrated  by 
these  compounds.  For  the  determination  of  the  solubility  of 
these  salts  in  acids,  they  were  finely  powdered,  and  saturated 
solutions  were  then  prepared  by  digesting  a  mixture  of  the 
acid  and  an  excess  of  the  salt  for  about  a  week,  at  ordinary 
temperature.  This  was  done  in  a  closed  flask.  Weighed  por- 
tions of  these  solutions  were  evaporated  to  dryness  and  the 
residues  dried  at  100°  and  weighed.  These  solubilities  were 
all  taken  at  22° ,  and  the  results  are  the  average  of  two  or  more 
closely  agreeing  determinations. 

100  parts  HC1  100  parts  HC1 

Sp.  gr.  1.2  dissolve  Sp.  gr.  1.05  dissolve 

2RbCl.TeCl4    .     .     .     0.34  parts  13.09  parts 

2CsCl.TeCl4     .    .     .    0.05    "  0.78     " 

*  Loc.  cit. 

t  Ber.  d.  Chem.  Ges.,  viii,  9. 


POTASSIUM,  RUBIDIUM,  AND  CAESIUM.  273 

100  parts  HBr  100  parts  HBr 

8p.  gr.  1.49  dissolve          8p.  gr.  1.08  dissolve 

2KBr.TeBr4     .     .     .     6.57  parts  62.90  parts 

2RbBr.TeBr4    .     .     .    0.25     «  3.88     " 

2CsBr.TeBr4     .     .     .     0.02     «  0.13     " 

The  double  tellurium  chlorides,  described  in  this  article, 
are  more  soluble  than  the  bromides,  and  the  bromides  more 
soluble  than  the  iodides.  The  solubility  of  these  compounds 
in  strong  alcohol  shows  the  same  gradation  as  their  solubility 
in  acids,  the  csesium  salts  being  practically  insoluble  in  this 
menstruum,  while  the  rubidium  salts  dissolve  to  a  trifling  but 
clearly  perceptible  extent,  and  the  potassium  salts  dissolve 
considerably  or  are  decomposed  with  separation  of  the  potas- 
sium halide,  or  both  solution  and  decomposition  take  place, 
according  to  the  salt  experimented  with. 

The  Chlorides. 

The  crystals  of  the  three  chlorides  have  a  pale  yellow  color, 
resembling  that  of  the  well-known  ammonium  phosphomo- 
lybdate  precipitate,  the  shade  becoming  somewhat  lighter  from 
the  caesium  to  the  potassium  salts. 

Ccesium  Tellurichloride,  20sQLTeCl^ — In  the  preparation 
of  this  compound,  and  also  in  the  preparation  of  the  rubidium 
and  potassium  double  chlorides,  the  tellurium  tetrachloride  is 
most  conveniently  made  by  converting  tellurium  into  tellurous 
oxide  by  means  of  aqua  regia,  evaporating  to  dryness  to  expel 
nitric  acid  and  then  dissolving  the  residue  in  hot  hydrochloric 
acid.  An  aqueous  solution  of  csesium  chloride,  added  to  this, 
produces  a  precipitate,  even  in  quite  dilute  solutions.  There 
must  be  an  excess  of  hydrochloric  acid  present  to  prevent  the 
separation  of  tellurous  acid.  On  boiling  and  adding  more 
water,  if  necessary,  this  precipitate  dissolves.  The  solution, 
left  to  cool,  deposits  small  brilliantly  lustrous  octahedra.  It 
is  a  general  fact,  with  these  double  halides,  that  an  excess  of 
one  or  the  other  of  the  constituents  does  not  affect  their  com- 
position. This  is  shown  in  this  particular  case  by  the  fact 
that  it  can  be  recrystallized  from  strong  solutions  of  tellurium 

or  of  csesium  chlorides. 

18 


43.44 

43.90 

44.63 

44.04 

20.65 

.  .  . 

21.41 

20.69 

35.93 

35.14 

.  .  . 

35.27 

274         DOUBLE  HALIDES   OF  TELLURIUM  WITH 


Cs   .    .    . 

Te  .     .    . 

Cl   .    .    . 

This  compound  is  perfectly  stable  in  the  air.  It  does  not 
melt  below  the  boiling-point  of  sulphuric  acid.  It  can  be 
precipitated  from  its  solution  in  dilute  hydrochloric  acid  by 
the  addition  of  concentrated  hydrochloric  acid.  A  portion  of 
the  salt,  finely  pulverized,  was  treated  with  water  at  ordinary 
temperature.  This  produced  a  voluminous  white  precipitate, 
which  was  washed  with  cold  water  and  dried  in  the  air. 


Te    . 

Analysis  gave 

....    71.43 

Calculated  for 
H2TeO8. 

71.43 

H20 
O     . 

....      7.52 
....     17.76 

10.29 
18.28 

Cl    . 

....      2.49 

Cs 

0.80 

The  oxygen  which  was  not  given  off  in  the  form  of  water 
on  heating  the  substance  was  calculated  by  difference.  From 
the  above  analysis  the  conclusion  may  be  drawn,  that  the  pre- 
cipitate produced  by  the  action  of  water  on  this  salt  is  essen- 
tially tellurous  acid,  a  small  amount  of  oxychloride  of  tellurium 
being  present.  Hot  water  dissolves  some  of  this  tellurous 
acid,  and,  on  cooling  slowly,  the  anhydride  separates  in  the 
characteristic  form  of  colorless  octahedra. 

Rubidium  Tellurichloride,  2RbCl.TeCl^  —  The  preparation 
of  this  salt  was  in  every  way  analogous  to  that  of  the  caesium 
tellurium  chloride.  However,  since  this  salt  is  far  more  solu- 
ble than  the  corresponding  caesium  compound,  no  precipitate 
was  obtained  in  dilute  solutions.  The  mixture  of  the  hydro- 
chloric acid  solution  of  the  constituents  was  concentrated  by 
evaporation,  and,  when  cooled,  crystals  separated.  These 
were  in  the  form  of  octahedra,  somewhat  larger  than  the 
caesium  salt. 


Kb  .     .     . 

Analysis  gave 

.    .    33.50        33.83 

Calculated  for 
2RbCl.TeCl4. 

3359 

Te   .     .    . 

.    .    24  34 

2456 

Cl    , 

41.85 

POTASSIUM,  RUBIDIUM,  AND   CESIUM.  275 

This  salt  remains  permanent  in  the  air.  From  the  dilute 
hydrochloric  acid  solution,  concentrated  hydrochloric  precipi- 
tates it  unaltered.  Water  decomposes  it,  evidently  in  the 
same  way  as  the  caesium  salt. 

Potassium  Tellurichloride,  2KOLTeCl^  —  To  prepare  this 
salt  in  a  pure  state  an  excess  of  tellurium  chloride  is  necessary. 

The  analyzed  material  was  obtained  by  spontaneous  evapora- 
tion of  the  constituents  in  a  solution  of  dilute  hydrochloric 
acid,  twice  as  much  tellurium  chloride  being  present  as  re- 
quired by  the  formula.  Under  these  conditions  it  was  found 
to  separate  in  the  form  of  light  yellow  octahedra,  which, 
under  the  microscope,  were  shown  to  be  free  from  potassium 
chloride. 

Analysis  gave  Calculated  for 

Ratio.  2KCl.TeCl4. 

K 17.37  0.44  18.79 

Te 30.29  0.24  30.03 

Cl 49.47  1.39  51.18 

97.13 

The  salt,  therefore,  has  the  formula  2KCl.TeCl4.  The 
crystals  deliquesce  somewhat  in  moist  air,  and  the  analyzed 
material  retained  a  small  amount  of  water,  as  is  shown  by  the 
deficiency  in  the  above  analysis.  It  is  not  probable  that  the 
salt  contains  water  of  crystallization,  for  the  crystalline  form 
and  optical  properties  show  that  it  is  isomorphous  with  the 
anhydrous  salts.  This  salt  is  the  most  unstable  as  well  as  the 
most  soluble  of  the  anhydrous  double  halides  described  in  this 
article.  It  is  readily  dissolved  by  dilute  hydrochloric  acid. 
Strong  hydrochloric  acid  separates  potassium  chloride.  It 
therefore  cannot  be  precipitated  from  its  solutions  by  the  addi- 
tion of  strong  hydrochloric  acid,  as  in  the  case  of  the  other 
chlorides.  Alcohol  also  separates  potassium  chloride.  Water 
apparently  effects  the  same  decomposition  as  in  the  case  of  the 
caesium  and  rubidium  chlorides.  The  tendency  of  potassium 
chloride  to  separate  along  with  the  salt  explains  why  Rammels- 
berg's  analysis  came  high  in  regard  to  the  potassium  chloride. 
His  results  corresponded  to  a  mixture  of  two  molecules  of  KC1 
and  three  molecules  of  2KCl.TeCl4.  Experiments  with  the 


276          DOUBLE  HALIDES  OF  TELLURIUM   WITH 

calculated  quantity  of  the  constituents  invariably  resulted  in 
the  separation  of  potassium  chloride  or  potassium  chloride 
mixed  with  the  yellow  2KCl.TeCl4.  Experiments  with  the 
method  given  by  Ramsay  *  for  the  preparation  of  this  salt,  by 
mixing  aqueous  solutions  of  the  constituents,  resulted  in  the 
decomposition  of  the  tellurium  chloride,  and  the  resulting 
white  precipitate  failed  to  dissolve  until  considerable  hydro- 
chloric acid  was  added.  Attempts  to  prepare  the  compound 
by  concentrating  the  mixture  of  the  constituents  by  the  aid 
of  heat  invariably  resulted  in  failure.  In  certain  cases,  on 
cooling  such  solutions,  a  mass  of  colorless  slender  prisms  was 
obtained,  which  have  not  yet  been  investigated. 

The  Double  Bromides. 

The  crystals  of  the  anhydrous  bromides  have  a  brilliant  red 
color  resembling  that  of  the  mineral  crocoite.  The  powders 
of  the  salts  have  a  color  that  is  similar  to  that  of  a  mixture  of 
equal  parts  potassium  bichromate  and  red  lead.  The  powder 
of  the  hydrous  bromide  has  the  color  of  mercuric  oxide,  but,  by 
loss  of  water  this  soon  changes  to  that  of  the  anhydrous  salt. 

Caesium  Telluribromide,  £  CsBr.  TeBr±.  —  This  double  halide 
can  easily  be  prepared  by  mixing  finely  divided  tellurium  with 
caBsium  bromide  in  dilute  hydrobromic  acid,  then  adding 
bromine  in  excess.  The  presence  of  free  acid  is  necessary  to 
prevent  the  separation  of  tellurous  acid.  When  the  tellurium 
has  disappeared,  the  solution  is  concentrated  by  the  aid  of 
heat,  and,  on  cooling,  bright  red  crystals  of  the  pure  salt  are 
deposited.  These  are  generally  somewhat  larger  than  the 
crystals  of  the  double  chloride. 

Analysis  gave  Calculated. 

Cs    .     .    .    30.90        30.87        30.91  30.54 

Te    .    .     .    14.29        13.60        14.03  14.35 

Br    .     .     .     55.01         .  .  .         55.32  55.11 

This  salt  remains  unaltered  in  the  air.  It  can  be  separated 
from  its  solution  in  dilute  hydrobromic  acid  by  the  addition 

*  Loc.  cit. 


POTASSIUM,  RUBIDIUM,  AND  CAESIUM.  277 

of  concentrated  acid.  It  does  not  melt  below  the  boiling- 
point  of  sulphuric  acid.  Attempts  to  prepare  a  hydrous 
salt  according  to  the  methods  used  for  the  preparation  of 
TeBr4 .2KBr.2HaO  were  without  success. 

Rubidium  Telluribromide,  2RbBr.TeBr^. — The  directions 
given  for  the  preparation  of  the  corresponding  csesium  com- 
pound apply  also  in  the  preparation  of  this  salt.  If  the  solu- 
tions are  strong,  the  compound  separates  as  a  bright  red 
precipitate,  but  if  dilute,  on  concentrating  by  means  of  heat 
or  spontaneous  evaporation,  it  crystallizes  in  brilliant  red 
octahedra. 

Analysis  gave  Calculated. 

Kb 22.02  22.04 

Te 16.11 

Br 62.07  61.85 

This  salt  is  stable  in  the  air.  Like  the  corresponding  caesium 
salt,  this  separates  from  its  solutions  by  the  addition  of  con- 
centrated hydrobromic  acid.  When  it  is  dissolved  in  a  little 
water  and  the  solution  is  cooled  slowly,  colorless  octahedrons 
of  TeO2  separate.  The  latter  product  was  found  to  be  impure, 
containing  a  small  amount  of  bromine.  On  heating,  the  salt 
decrepitates  slightly  and  melts  at  a  high  temperature.  Efforts 
to  prepare  a  hydrous  salt  according  to  the  methods  used  for 
the  preparation  of  2KBr.TeBr4.2H2O  were  without  success. 

Potassium  Telluribromides,  ^KBr.TeBr*  and  2KBr.TeBr^. 
2HZ0.*  —  For  the  preparation  of  these  salts,  a  mixture  of  the 
constituents  was  made  as  described  in  the  case  of  the  csesium 
double  bromide.  The  solution  invariably  deposited  crystals 
of  the  anhydrous  salt  when  it  had  been  concentrated  by  heat, 
but,  by  spontaneous  evaporation  of  the  filtrate,  the  hydrous 
salt  was  obtained.  On  recrystallizing  either  of  these  salts 
from  water  or  from  dilute  hydrobromic  acid,  the  anhydrous 
salt  is  obtained  when  the  solution  has  been  saturated  by  boil- 
ing and  then  allowed  to  cool,  but  if  the  solution  is  left  to 
deposit  crystals  at  ordinary  temperature  the  hydrous  modifica- 

*  Described  by  Von  Hauer  as  containing  three  molecules  of  water  of 
crystallization. 


278         DOUBLE  HALIDES   OF  TELLURIUM  WITH 

tion  is  obtained.  The  crystals  of  these  different  compounds 
closely  resemble  each  other  in  color  and  appearance.  The 
anhydrous  variety  crystallizes  in  octahedra  modified  by  the 
cube.  The  orthorhombic  crystals  of  the  hydrous  salt  look  like 
distorted  crystals  of  the  other.  This  being  the  case,  and  since 
the  crystals  of  the  hydrous  compound  can  be  obtained  much 
larger  than  those  of  the  anhydrous  salt,  both  Von  Hauer  and 
Wills  selected  these  for  their  work,  while  the  more  easily 
obtained  anhydrous  salt  was  overlooked.  The  hydrous  salt  is 
readily  distinguished  from  the  anhydrous  one  by  its  deport- 
ment on  exposure  to  a  dry  atmosphere.  The  latter  is  stable, 
but  under  these  conditions  the  hydrous  compound  rapidly 
effloresces,  losing  its  lustre,  the  faces  of  the  crystals  becoming 
superficially  covered  with  a  light  reddish  yellow  and  opaque 
layer  of  the  anhydrous  salt.  Crystals  which  have  been  ex- 
posed to  dry  air  for  several  days  and  were  completely  covered 
with  this  layer  were  found,  on  crushing,  to  remain  unaltered 
in  the  interior  and  to  have  still  retained  included  water  in 
addition  to  their  water  of  crystallization.  This  was  shown  by 
the  fact  that  the  crushed  crystals  gave  a  stain  of  the  mother- 
liquor  to  filter  paper.  This  property  of  the  hydrous  crystals 
explains  why  Von  Hauer  assigned  three  molecules  of  water  to 
this  salt  instead  of  two.  The  material  for  analysis  of  the 
hydrous  salt  was  selected  from  crystals  varying  in  size  from  7 
to  13mm.  in  diameter.  These  were  very  rapidly  crushed  on 
smooth  filter  paper,  to  remove  included  water,  and  immediately 
corked  up  in  the  weighing  tube  and  analyzed.  A  close  exam- 
ination of  the  fragments,  before  and  after  weighing,  gave  no 
evidence  of  loss  of  water  from  the  substance  by  efflorescence. 
The  analyses  were  from  three  different  crops. 

Analysis  gave  Calculated  for         Calculated  for 

2KBrTeBrv2H2O.  2KBr.TeBr4.3H2O. 


K    .  .  .  10.90  11.07  10.73  10.87  10.61 

Te  .  .  .  17.59  17.29  17.46  17.38  16.96 

Br  .  .  .  66.35  66.36  66.34  66.74  65.11 

H20  .  .  5.33  5.53  5.73  5.01  7.32 

These  results  make  it  evident  that  the  salt  contains  two  mole- 
cules of  water,  and  not  three  as  has  generally  been  supposed. 


POTASSIUM,  RUBIDIUM,  AND   CESIUM.  279 

The  water  in  this  salt  was  determined  by  heating  it  in  an  air 
bath  to  constant  weight.  The  temperature  was  maintained 
between  150°-160°,  and  finally,  to  be  sure  that  all  the  water 
had  been  driven  off,  the  residues  were  analyzed  in  two  cases. 


Analysis  gave 

K    .....     11.71        11.52  11.44 

Te  .....    18.29        18.58  18.30 

Br  .....    70.25        70.09  70.26 

Analyses  of  products  obtained  by  cooling  hot  saturated 
solutions  gave  the  following  results  : 

Found.  Calculated  for 
2KBrTeBr4. 


K    .     .     .     .     11.67        11.70         .  .  .  11.44 

Te  .     .     .     .    18.06         18.30 

Br  .     .     .    .    70.24        70.20        69.40  70.26 

The  Double  Iodides. 

These  salts  are  all  black.  The  powder  of  the  caesium  salt 
is  pure  black,  that  of  the  rubidium  and  potassium  salts  is 
grayish  black. 

Ccesium  Telluriiodide,  2  Osl.  Tel±.  —  In  order  to  prepare  this 
salt,  and  also  in  the  case  of  the  rubidium  and  potassium  com- 
pounds, tellurium  tetraiodide  was  made  by  treating  tellurous 
oxide  with  hydriodic  acid.  The  iodide  of  tellurium  is  spar- 
ingly soluble  in  hydriodic  acid,  but,  on  mixing  this  solution 
with  a  solution  of  csesium  iodide,  an  amorphous  black  precipi- 
tate was  obtained,  even  in  very  dilute  solutions. 

Anai-mn'a  «.  Calculated  for 

Analysis  gave  2CsLTeIi. 

Cs 23.37  23.07 

Te 10.51  10.84 

I 65.17  66.09 

This  compound  resisted  all  attempts  to  prepare  it  in  a  crys- 
talline form.  It  is  insoluble  in  csesium  iodide  and  in  hydriodic 
acid ;  hence  warming  in  the  mother-liquor  failed  to  dissolve  the 
salt.  It  is  decomposed  slowly  by  cold  water,  rapidly  by  hot, 
and  apparently  tellurous  acid  or  anhydride  separates.  This 
generally  is  impure,  being  mixed  with  a  dark-colored  residue 


280         DOUBLE  HALIDES  OF  TELLURIUM  WITH 

containing  iodine.  On  exposure  the  salt  slowly  loses  iodine. 
In  the  open  capillary  it  does  not  melt  below  the  boiling-point 
of  sulphuric  acid. 

Rubidium  Telluriiodide,  2KbLTeI^  —  This  compound  was 
prepared  by  mixing  the  constituents  in  the  same  manner  as  in 
the  preparation  of  the  corresponding  caesium  salt.  If  the  solu- 
tions are  only  moderately  concentrated,  a  black  amorphous  pre- 
cipitate is  produced.  Unlike  the  corresponding  caesium  salt,  it 
dissolves,  to  a  slight  extent,  on  warming  in  the  mother-liquor, 
and  on  cooling,  black  microscopic  octahedra  are  produced. 


Analysis  gave 

Eb   .....    16.83  16.17 

Te    ........  11.81 

I       .....    72.07  72.02 

This  iodide  is  stable  on  exposure.  Water  effects  the  same 
decomposition  as  in  the  case  of  the  caesium  salt.  A  small 
portion  of  this  salt  dissolves  in  strong  alcohol,  giving  the  color 
of  a  weak  iodine  solution. 

Potassium  Telluriiodide,  2KI.  TeI^Hz  0.  —  This  compound 
can  be  prepared  most  conveniently  by  boiling  tellurium  iodide 
in  a  strong  solution  of  potassium  iodide  in  dilute  hydriodic 
acid.  The  solution,  filtered  while  hot  from  any  undissolved 
tellurium  iodide,  deposits  long  black  prisms  on  cooling.  These 
crystals  attain  considerable  size,  about  30  mm.  in  length,  when 
a  large  excess  of  potassium  iodide  is  used.  The  mother-liquor, 
on  evaporation  in  a  desiccator,  deposits  more  of  the  salt,  but 
the  crystals  have  a  different  habit. 


K  .  .  . 
Te  .  .  . 
I  ... 

H20     .     . 

For  the  determination  of  water  in  this  compound  the  crystals 
were  rapidly  pressed  on  paper  and  immediately  analyzed.  It 
was  found  that  the  salt  could  be  dehydrated  at  a  temperature 


Analysis  gave 

Calculated  for 
2KI.TeI4.2H20. 

7.81 

8.41 

8.50 

8.39 

12.25 

12.95 

12.30 

12.48 

75.97 

... 

76.68 

76.11 

3.57 

... 

.  •  • 

3.60 

POTASSIUM,  RUBIDIUM,  AND   CAESIUM. 


281 


between  110°-115°,  the  resulting  anhydrous  salt  being  stable 
at  that  temperature.  This  was  shown  by  an  iodine  determina- 
tion in  the  residue.  Analysis  gave  78.78  per  cent  of  iodine ; 
calculated  for  2KI.TeI4,  78.94. 

This  salt  is  far  more  stable  in  the  air  than  the  corresponding 
bromide,  but  the  crystals  lose  their  lustre  in  dry  air,  becoming 
dull  black  on  account  of  a  superficial  efflorescence. 

Crystallography. 

The  crystallization  of  the  anhydrous  alkali-tellurium  halides 
is  isometric.  The  chlorides  were  obtained  in  octahedra  with 
little  or  no  modification,  the  bromides  in  combination  of  octa- 
hedron and  cube.  The  chlorides  and  bromides  were  measured, 
and  also  proved  to  be  isotropic  by  examination  in  polarized 
light.  Of  the  anhydrous  iodides,  the  rubidium  salt  was  the 
only  one  obtained  in  crystals,  and  these  were  too  small  to 
measure,  but  appeared  under  the  microscope  as  combination  of 
octahedron  and  cube.  They  were  so  opaque  that  they  could 
not  be  tested  in  polarized  light. 

The  two  hydrous  salts  2KBr.TeBr4.2H2O  and  2KLTeI4. 
2H2O,  although  analogous  to  each  other  in  their  composition, 
differ  in  crystallization.  The  bromide  is  orthorhombic,  as  has 
been  shown  by  Baker,*  also  by  Grailich  and  Lang  in  Rammels- 
burg's  Handbuch.*  That  the  hydrous  potassium  tellurium 


m 


*  Loc.  cit. 


282  DOUBLE  HALIDES  OF  TELLURIUM. 

bromide  obtained  in  the  present  work  is  identical  with  that 
described  by  the  above  authors  is  shown  by  measurements  of 
the  crystals.  The  crystallization  of  the  salt  2KI.TeI4.2H2O  is 
monoclinic.  Two  different  habits  were  observed ;  long  prisms, 
developed  in  the  direction  of  the  clino  axis  were  obtained  from 
hot  solutions  (Fig.  1).  The  mother-liquor  from  these,  on 
standing,  gave  shorter  prisms  in  which  the  domes  and  clino- 
pinacoids  were  wanting  (Fig.  2). 
The  forms  observed  were : 

m,  110  c,  001  d,  031 

p,  111  b,  010 

The  axial  ratio  is  as  follows : 

a  :  b  :  6  0.7047 ;  1 ;  0.5688  B  =  100  A  001  =  59°  7'  16" 

The  crystals  gave  fair  reflections  of  the  signal  on  the  goni- 
ometer. Measurements  chosen  as  fundamental  are  indicated 
by  an  asterisk. 


Calculated. 

Measured. 

Wl  A  Wl"' 

,  110  A  1TO 

62°  20' 

62°  26' 

m  A  bj 

110  A  010 

58°  50' 

*58°  50' 

b  AC, 

010  A  001 

90° 

90° 

m  A  c} 

110  A  001 

63°  57' 

*63°  57' 

m  A  p, 

110  A  11T 

60°  42' 

*60°  42' 

c  Ap, 

001  A  Til 

55°  21' 

55°  22' 

b  Ad, 

010  A  031 

34°  20' 

34°  25' 

b  AP, 

010  A  11T 

61°  42'  49" 

61°  42'  30" 

m  A  w', 

110  A  T10 

117°  40' 

117°  33' 

c  A  mf, 

001  A  T10 

116°  3' 

116°  11' 

The  crystals  were  too  opaque  for  any  optical  examination. 

In  conclusion  the  author  wishes  to  express  his  indebtedness 
to  Prof.  H.  L.  Wells  for  valuable  advice  and  for  the  interest 
that  he  has  taken  in  this  work,  and  to  Prof.  S.  L.  Penfield 
under  whose  direction  the  crystallography  of  these  salts  was 
investigated. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
January,  1893. 


ON  THE  AMMONIUM-LEAD  HALIDES.* 

BY  H.  L.  WELLS  AND  W.  K.  JOHNSTON. 

IT  is  a  well-known  fact  that  the  ammonium  double  halides, 
like  other  ammonium  salts,  are  usually  analogous  to  those  of 
the  alkali  metals,  especially  to  those  of  potassium.  For  ex- 
ample, in  connection  with  an  investigation  of  the  caesium- 
mercuric  halides,  made  by  one  of  us,  f  it  was  noticeable  that 
caesium  compounds  were  prepared,  corresponding  to  all  of  the 
four  types  of  ammonium-mercuric  halides  that  had  been  pre- 
viously described. 

A  study  of  the  caesium-lead  and  potassium-lead  halides  has 
recently  been  made  in  this  laboratory,  J  and,  in  view  of  the 
fact  that  the  existence  of  four  very  simple  types  of  double 
salts  was  established  by  that  investigation,  it  seemed  desirable 
to  re-investigate  the  ammonium-lead  halides,  since  a  consider- 
able number  of  these  with  very  complicated  formulae  had  been 
described.  These  peculiar  ammonium-lead  halides  have  formed 
the  most  noticeable  exception  to  the  similarity  of  the  alkali- 
metal  and  ammonium  salts,  and  it  seems  probable  that  it  was 
chiefly  on  account  of  these  that  Remsen  has  remarked :  §  "  The 
position  of  the  double  halides  containing  ammonium  is  certainly 
exceptional.  They  seem  to  be  governed  by  some  law  of  their 


own." 


All  of  the  extremely  complicated  ammonium-lead  salts  have 
been  described  by  Andre*.  || 

The  list  of  his  alleged  compounds  is  as  follows : 

*  Amer.  Jour.  Sci.,  xlvi,  July,  1893. 

t  Ibid.,  xliv,  221.  I  Ibid.,  xlv,  121. 

§  Amer.  Chem.  Jour.,  xi,  296. 

||  Compt.  Kend.,  xcvi,  435  and  1502 ;  Bull.  Soc.  Chim.,  (2),  xl,  14. 


284  ON  THE  AMMONIUM-LEAD  HALIDES. 

PbCl2.18NH4C1.4H20  2PbBr2.14NH4Br.3H20 

PbCl2.10NH4Cl.HaO  PbBr2.6NH4Br.H20 

2PbCl2.18NH4C1.3H20  7PbBr2.12NH4Br.7H20 

PbCl2.6NH4Cl.H20  3PbBr2.2NH4Br.H20 

4PbCla.22NH4C1.7H20  

4PbCl2.18NH4C1.5H20  

4PbCl2.2KE4C1.6H20  

From  Andre's  original  articles,  it  appeared  that  he  made  no 
mention  of  having  ever  prepared  any  of  his  remarkable  prod- 
ucts more  than  once,  and  it  seems  probable  that  whenever  he 
obtained  a  crop  of  crystals  or  a  precipitate  he  described  it  as 
a  new  compound,  without  regarding  the  number  of  different 
substances  that  it  might  contain.  Andre*  operated  in  two 
ways.  A  part  of  his  salts  were  made  by  dissolving  a  lead 
halide  in  a  hot  solution  of  the  corresponding  ammonium 
halide  and  cooling,  while  the  rest  were  made  by  dissolving 
lead  monoxide  in  boiling  solutions  of  ammonium  chloride  or 
bromide.  From  the  products  made  by  the  last  method  he 
obtained  lead  oxychlorides  or  oxybromides  by  heating  them 
with  water  in  sealed  tubes.  This  peculiarity  of  these  products 
caused  him  to  remark  that  all  the  chlorides  made  in  this  way 
seemed  to  contain  some  oxychloride.  This  is  the  only  evi- 
dence of  any  suspicion  on  his  part  that  he  was  obtaining  mix- 
tures. In  a  number  of  instances  Andre*  describes  his  products 
as  "crystalline  precipitates,"  "  brilliant  plates  with  pearly 
lustre,"  "  crystallized  bodies,"  etc.,  so  that  it  would  seem  that 
they  should  have  been  pure,  but  after  having  repeated  his  ex- 
periments, following  his  methods  as  closely  as  his  descriptions 
permitted,  with  many  variations  and  repetitions,  we  are  con- 
vinced that  not  one  of  the  salts  described  by  Andre  exists. 

Our  work  has  resulted  in  the  preparation  of  the  following 
series  of  salts : 

Type  2  : 1.  Type  1  :  1.  Type  1  :  2. 

3NH4PbCl8.H2O  NH4Pb2Cl6 

(NH4)2PbBr4.H20  NH4Pb8Br6 

NH4PbI8.2H2O  


ON  THE  AMMONIUM-LEAD  HALIDES.  285 

For  comparison,  the  potassium  series,  already  referred  to,  is 
given: 

Type  2  : 1.  Type  1  : 1.  Type  1  :  2. 

3KPbCl8.H20  KPb2Cl5 

K2PbBr4.H20  3KPbBr8.H20  KPb2Br5 

KPbBr8.H2O  .... 

KPbI3.2H20  .... 

It  is  to  be  noticed  that  the  two  series  correspond  exactly,  ex- 
cept that  no  ammonium-lead  bromide  of  the  1:  1  type  was 
obtained.  These  results  show  that  the  ammonium-lead  halides 
are  entirely  analogous  to  the  potassium  salts,  and  that  there  is 
no  indication  that  they  are  governed  by  a  law  of  their  own. 

Returning  to  the  mixtures  described  as  compounds  by  An- 
dre", it  should  be  noticed  that  he  came  near  finding  the  correct 
formula)  for  three  salts.  His  formula  4PbCl22NH4C1.6H2O 
would  be  correct  if  the  water  were  omitted.  He  should 
have  found  two  more  molecules  of  NH4Br  in  the  formula 
7PbBr2.12NH4Br.7H2O  in  order  to  have  the  salt  (NH4)2PbBr4 
H2O,  and  his  formula  3PbBr2.2NH4Br.H2O,  in  comparison 
with  the  errors  involved  in  his  more  complicated  mixtures,  is 
rather  near  NH4Pb2Br6. 

Such  work  as  Andrews  is  liable  to  hinder  the  development 
of  correct  chemical  theories.  A  case  has  been  mentioned 
above  where  it  is  probable  that  his  results  have  been  an  im- 
portant factor  in  causing  the  ammonium  double  halides  to  be 
looked  upon  as  a  class  of  bodies  distinct  from  the  alkali-metal 
compounds,  and  it  may  be  mentioned  that  Carnegie  *  has  used 
Andrews  formula  PbBr2.6NH4Br  in  support  of  a  theory  on 
double  halides,  although,  as  must  be  added,  he  considers 
Andrews  more  complicated  formulae  as  inconsistent  with  his 
ideas. 

We  have  investigated  the  ammonium-lead  halides  by  meth- 
ods which  ( are  entirely  like  those  used  for  the  potassium  salts, 
and,  in  addition,  numerous  experiments  have  been  made  in 
order  to  investigate  Andrews  methods  of  preparation.  The 

*  Amer.  Chem.  Jour.,  xv,  11. 


286  0^  THE  AMMONIUM-LEAD  HALIDES. 

analytical  methods  used  have  been  simple.  Ammonium  was 
determined  by  distillation  with  potash  solution  and  alkalime- 
try. Lead  was  determined  by  treating  the  substance  in  a 
platinum  crucible  with  sulphuric  acid,  evaporating,  igniting 
and  weighing  lead  sulphate.  To  determine  a  halogen,  the 
substance  was  treated  with  hot  water  and  an  excess  of  silver 
nitrate  was  added  ;  after  sufficient  digestion,  nitric  acid  was 
added,  and  when  the  precipitate  had  settled  properly  it  was 
collected  and  weighed  on  a  Gooch  filter.  Water  was  deter- 
mined by  the  loss  at  100°,  or  sometimes  at  a  somewhat  higher 
temperature. 

1  :  1  Ammonium-Lead  Chloride,  SNHfl  C13.H2O.  —  This 
is  formed  by  dissolving  lead  chloride  in  hot  concentrated  solu- 
tions of  ammonium  chloride  and  cooling.  Sample  A  was 
made  by  dissolving  25  g.  of  PbCl2  in  700  c.  c.  of  an  ammonium 
chloride  solution  which  was  more  than  saturated  when  cold. 
The  double  salt  was  deposited  in  the  form  of  colorless,  trans- 
parent, prismatic  crystals  while  the  solution  was  still  some- 
what warm.  Some  of  the  crystals  were  removed  from  the 
warm  solution,  quickly  pressed  between  smooth  filter-papers 
and  air-dried  for  analysis.  On  cooling  the  solution,  ammo- 
nium chloride  crystallized  upon  the  double  salt.  Sample  B  was 
obtained  by  dissolving  5  g.  of  PbO  in  200  c.  c.  of  a  boiling  solu- 
tion of  NH4C1  which  was  nearly  cold-saturated.  The  last 
method  was  suggested  by  Andrews  experiments. 

Calculated  for 
x        3NH4PbCls.H,0. 


Ammonium    .     .  5.22-  5.45          .  .....  5.33 

Lead     ....  61.12-60.60  61.84-61.88  61.31 

Chlorine    .     .     .  31.78-31.79              31.64  31.56 

Water   ....  1.78               ......  1.78 

The  water  in  A  was  determined  by  heating  at  about  120° 
for  one  hour.  The  limits  of  the  conditions  under  which 
this  salt  is  formed  are  narrow,  for,  on  slightly  diluting  the 
solutions  which  have  given  it,  the  following  compound  is 
produced. 

1  :  2  Ammonium-Lead    Chloride,    Nff^Pb^Cl,.—  This  salt 


ON  THE  AMMONIUM-LEAD  HALIDES. 


287 


is  produced  under  wide  limits  of  conditions.     It  forms  color- 
less,  short,   transparent    prisms  which   are    usually  doubly 
terminated  and  are  apparently  orthorhombic  in  form.     The 
crystals  retain  their  lustre  on  drying  and  are  anhydrous. 
Four  crops  were  made  under  the  following  conditions : 


A 
B 
C 
D 


NH4C1. 

g- 

100 
100 
200 
200 


PbCl2. 

g- 

30 

20 
15 
60 


Volume, 
c.  c. 

1000 

1000 

550 

700 


These  crops  gave  the  following  analyses : 


A    

Ammonium. 

2.36-2.67 

Lead. 

67.38-67.36 

Chlorine. 

29.08-29.14 

B         .     .     .    . 

66  26-67.56 

C     

66.94-66.76 

29.16-29.24 

D    

68.00-67.28 

Calculated  for  | 
NH4Pb2Cl5    j 

2.95 

67.93 

29.12 

Another  double  chloride  was  observed,  the  composition  of 
which  was  not  determined.  It  will  be  referred  to  beyond, 
under  the  discussion  of  Andrews  products. 

2:1  Ammonium-Lead  Bromide,  (Nff4)2Pb£r4.H20. — This 
salt  is  easily  prepared  by  dissolving  lead  bromide  in  concen- 
trated solutions  of  ammonium  bromide.  Its  formation  was 
also  observed  when  lead  oxide  was  dissolved  in  ammonium 
bromide  by  boiling.  It  forms  beautiful  radiating  groups  of 
highly  refracting,  slender  prisms.  Three  crops  were  made  as 
follows : 


A 
B 
C 


NH4Br. 

200 
? 

200 


PbBr, 
g. 

50 
25 

50 


Volume, 
c.  c. 

380 
260 
380 


288  ON  THE  AMMONIUM-LEAD  HALIDES. 

The  analyses  were  as  follows  : 

Ammonium.  Lead.  Bromine.  Water. 

A    .....    6.01-5.86    37.12-36.84    55.06-55.10    2.60 

B     ........        37.06-36.94         54.94 

C     ........  37.26  ...... 

65-08    3-10 


1  :  2  Ammonium-Lead  Bromide,  Nff4Pb2jBr5.  —  On  slightly 
diluting  solutions  from  which  the  preceding  salt  would  be 
deposited,  this  salt  is  obtained.  Repeated  trials  were  made  to 
obtain  a  1  :  1  salt  intermediate  between  the  two,  but  these 
were  without  success.  The  salt  forms  square  plates,  often 
several  millimeters  in  diameter.  The  crystals  darken  some- 
what on  exposure  to  light,  but  they  do  not  lose  their  lustre  on 
drying,  and  are  evidently  originally  anhydrous.  The  com- 
pound is  formed  under  rather  wide  limits  of  conditions.  A 
single  sample  was  analyzed. 

,,       A  Calculated  for 

Pound.  NH4Pb2Br6. 

Ammonium  .     .     .       2.17-  2.17  2.16 

Lead     .....    49.26-49.12  49.76 

Bromine    ....     48.28-48.22  48.08 


1:1  Ammonium-Lead  Iodide,  Nff^Pbl^HzO.  —  This  was 
the  only  double  iodide  obtained,  although  a  thorough  search 
was  made  for  other  salts.  It  forms  hair-like  crystals  of  a  pale 
yellow  color.  Sample  A  was  made  by  dissolving  100  g.  of 
NH4I  and  10  g.  of  PbI2  in  sufficient  hot  water  to  make  a  volume 
of  108  c.  c.,  and  cooling.  Sample  B  was  obtained  by  slightly 
diluting  the  solution  which  gave  A.  It  was  noticed  that 
where  lead  iodide  was  deposited  from  a  moderately  concentrated 
hot  solution  of  ammonium  iodide,  the  lead  iodide  disappeared 
on  cooling  and  in  its  place  was  formed  a  compact,  silky  mass  of 
crystals.  Sample  C  was  such  a  crop  as  just  described,  which 
was  carefully  separated  from  the  usual  form  of  the  double  salt 
which  formed  above  in  the  solution. 


ON  THE  AMMONIUM-LEAD  HALIDES.  289 


Ammonium  . 

Calculated  for 
NH4PbI3.2H2O. 

2.80 

A. 

.      2.40-  2.25 

B. 

2.97-  2.97 

c. 

Lead   .    .    . 

.     31.08-31.46 

31.36-31.20 

31.76 

32.24 

Iodine      .     . 

.     59.76-59.70 

59.85-59.75 

62.45 

59.36 

Water 

5.60 

5.65 

•  •  . 

5.60 

On  Andre's  Products. 

Andre*  prepared  some  of  his  most  complicated  products,  such 
as  2PbCl4.18NH4C1.3H2O  and  4PbC1.22NH4C1.7H2O,  by  dis- 
solving lead  chloride  in  ammonium  chloride  solutions  and  by 
the  use  of  the  corresponding  bromides.  On  repeating  his  ex- 
periments with  the  bromides,  we  have  not  observed  anything 
which  did  not  correspond  to  the  salts  which  we  have  described, 
or  to  mixtures  of  these  with  ammonium  bromide.  He  de- 
scribes his  product  4PbCl2.  22NH4C1.7H2O  as  an  abundant  pre- 
cipitate of  very  brilliant  plates  with  a  pearly  lustre.  We  have 
often  observed  this  beautiful  precipitate,  but,  after  many 
attempts,  we  have  been  unable  to  determine  its  composition 
with  certainty.  It  apparently  forms  only  in  warm  solutions 
which  are  almost  saturated  with  ammonium  chloride.  The 
prismatic  salt  NH4Pb2Cl5  is  usually  deposited  just  before  the 
plates  begin  to  form,  and  it  often  forms  with  them.  Large 
amounts  of  ammonium  chloride  often  crystallized  out  when 
attempts  were  made  to  separate  the  precipitate  from  the  mother- 
liquor.  This  happened  often  even  when  the  solution  with  the 
suspended  precipitate  was  poured  upon  a  large  mass  of  filter- 
paper,  so  as  to  soak  up  the  liquid  as  quickly  as  possible.  Such 
a  crop,  which  was  granular  and  showed  little  evidence  of  being 
composed  of  plates,  gave  30.50  per  cent  of  lead.  By  collect- 
ing the  precipitates,  in  the  manner  just  described,  at  an  earlier 
period  in  the  process  of  their  formation,  we  succeeded  in 
obtaining  crops  that  were  apparently  pure,  but  the  plates  were 
so  exceedingly  thin  and  small,  and  the  mother-liquor  was  so 
concentrated,  that  we  had  little  confidence  in  the  purity  of 
these  products.  Two  such  crops  gave  51.13  and  53.69  per 
cent  of  lead.  The  formula  (NH4)2PbCl4  requires  53.77,  and 
it  is  possible  that  this  may  be  the  true  f  ormula  for  the  sub- 

19 


290  ON  THE  AMMONIUM-LEAD  HALIDES. 

stance.  It  is  certain  that  these  two  products  were  practically 
free  from  the  prismatic  salt  NH4Pb2Cl6,  so  that  it  can  be  posi- 
tively stated  that  the  ratio  of  ammonium  to  lead  cannot  be 
greater  than  2  :  1  in  this  compound.  Andrews  formula  is, 
therefore,  very  far  from  correct.  He  must  have  analyzed  a 
mixture  of  the  plates  with  ammonium  chloride.  We  have 
found  all  such  mixtures  to  be  anhydrous  after  being  dried  in 
the  air  for  a  short  time,  hence  the  water  in  Andrews  formula  is 
remarkable. 

A  number  of  attempts  were  made  to  obtain  the  compound 
in  a  purer  state  by  warming  the  solutions  and  by  diluting  them 
slightly,  after  the  precipitates  had  formed,  but  these  operations 
left  the  products  open  to  suspicion,  since  it  was  found  that 
further  dilution  completely  decomposed  the  plates.  Several 
crops,  made  in  this  way,  gave  59.01,  57.64,  53.69,  and  57.80 
per  cent  of  lead,  which  is  an  insufficient  amount  for  the  1  :  1 
anhydrous  salt,  requiring  62.4.  This  may  be  its  composition, 
but  it  is  possible  also  that  it  is  a  dimorphous  form  of 
NH4Pb2Cl5,  for  the  plates,  in  being  square  with  diagonal  mark- 
ings, resemble  the  salt  KPb2Br6  and  other  bromides  of  this  type. 
The  undetermined  double  chloride  can  be  readily  prepared  by 
dissolving  160  g.  of  ammonium  chloride  and  25  g.  of  lead  chlo- 
ride in  sufficient  boiling  water  to  make  a  volume  of  400  c.  c. 
and  allowing  the  solution  to  cool  slowly.  The  compound 
often  forms  in  such  abundance  as  to  completely  fill  the  solution 
with  a  loose  mass  of  the  very  thin  plates. 

Andrews  other  method  of  preparing  his  products  was  by  dis- 
solving lead  monoxide  in  ammonium  chloride  and  bromide 
solutions.  He  describes  only  one  complicated  bromide,  PbBr2. 
6NH4Br.H2O,  made  in  this  way.  We  have  made  a  number  of 
experiments  with  ammonium  bromide  and  lead  oxide  without 
obtaining  anything  but  our  own  salts  and  mixtures.  Since  a 
number  of  his  chlorides  were  made  by  dissolving  lead  oxide  in 
ammonium  chloride  solutions,  we  have  made  a  very  careful 
study  of  the  products  obtained  by  this  operation.  Andre* 
sometimes  indicates  the  length  of  time  of  boiling  the  ammo- 
nium chloride  solution  with  lead  oxide,  but  is  uncertain  how 


ON  THE  AMMONIUM-LEAD  HALTDES.  291 

rapidly  he  boiled  his  solutions.  We  have  therefore  made 
numerous  experiments  with  wide  variations  in  the  amount  of 
ammonia  boiled  off.  Among  the  various  products  that  we 
obtained,  including  the  salts  that  we  have  described,  we  fre- 
quently noticed  a  substance  that  appeared  to  be  new.  It  was 
deposited  after  the  solutions  had  become  cold  or  nearly  so, 
forming  brilliant  crystals,  apparently  nearly  cubic  in  form,  but 
so  much  rounded  as  to  have  no  distinct  faces.  These  crystals 
were  often  1  or  2  mm.  in  diameter.  They  formed  upon  the  bot- 
tom and  sides  of  the  beaker,  adhering  firmly  to  the  glass,  and 
their  quantity  was  sometimes  such  that  the  walls  of  the  vessel 
were  thickly  studded  with  them.  This  product  evidently 
corresponded  with  one  of  Andrews,  for  he  says  of  "  PbCl2. 
18NH4C1.4H2O "  that  it  is  a  very  hard  crystalline  deposit 
adhering  to  the  glass.  We  encountered  considerable  difficulties 
in  obtaining  the  substance  in  a  pure  condition,  for  it  was  in- 
clined to  deposit  upon  other  things  that  had  previously  formed, 
and  it  adhered  to  them  as  well  as  to  the  glass.  The  first  crop 
analyzed  (No.  1)  was  evidently  not  pure.  Two  other  crops 
(2  and  3)  appeared  better,  but  still  not  quite  pure.  At  last,  by 
decanting  a  solution  just  before  these  crystals  began  to  form, 
we  obtained  a  crop  (No.  4),  that  seemed  entirely  satisfactory. 
The  following  analyses  of  the  four  crops  were  made: 

Chlorine. 

58.05  =  99.77 


No.  1 
No.  2 

Ammonium. 

.    .     .    28.28 

Lead. 

13.44 
6.51 

No.  3 

No.  4 



6.74 
1.08 

The  crystals  of  the  last  product  had  exactly  the  same  appear- 
ance as  the  others.  It  is  evident  that  lead  is  not  an  essential 
constituent  of  the  substance,  and  that  the  substance  is  am- 
monium chloride  crystallized  in  an  unusual  form.  Analysis 
No.  1  corresponds  to  PbCl2.24NH4Cl.  This  is  not  far  from 
Andrews  formula,  and  it  shows  what  he  probably  analyzed.  It 
is  to  be  noticed  that,  while  our  impure  ammonium  chloride 
was  practically  anhydrous,  Andre*  gives  a  considerable  amount 


292  ON  THE  AMMONIUM-LEAD  HAL1DES. 

of  water  in  his  formula.  It  seems  probable  that  he  did  not 
properly  dry  his  products  before  analyzing  them,  and,  more- 
over, he  evidently  determined  water  from  the  deficiencies  in 
his  analyses.  There  is  more  or  less  water  in  every  one  of  his 
formulae. 

Since  it  was  evident  that  Andrews  operation  of  boiling  am- 
monium chloride  solutions  with  lead  oxide  could  be  imitated, 
with  possibilities  for  greater  variations,  by  adding  ammonia  to 
solutions  of  lead  chloride  in  ammonium  chloride,  we  have  car- 
ried out  a  series  of  experiments  on  that  plan.  No  indications 
of  the  existence  of  any  of  Andrews  complicated  compounds 
were  obtained  in  this  way,  but,  besides  the  form  of  ammonium 
chloride  that  adheres  to  the  glass,  a  peculiar  modification  of  it 
in  the  form  of  large,  transparent  pointed  crystals  with  no  dis- 
tinct faces  was  observed.  A  sample  of  these  contained  3.23 
per  cent  of  lead.  When  much  ammonia  was  used  in  these 
experiments,  an  oxychloride  of  lead  was  obtained.  A  pure 
product  of  this  was  prepared  by  saturating  a  cold-saturated 
solution  of  ammonium  chloride  with  lead  chloride  while  boiling, 
then  adding  an  equal  volume  of  the  cold-saturated  ammonium 
chloride  solution  and  finally  adding  a  large  excess  of  ammonia. 
A  precipitate  was  formed  and  re-dissolved  by  the  ammonia. 
The  oxychloride  was  deposited,  on  cooling,  in  the  form  of  small, 
blade-like,  transparent  crystals.  Analysis  showed  that  it  was 
the  compound  PbClOH. 


Calculated  for 
PbClOH. 


Lead  ......  79.17  79.77 

Chlorine       ....  14.06  13.68 

Oxygen   .....  [2.72]  3.08 

Water     .....  4.05  3.47 

This  compound  has  long  been  well  known,  having  been  used 
as  a  white  pigment.  It  is  worthy  of  remark  that  Andre*  re- 
described  this  body  correctly  in  one  of  his  papers  that  has 
already  been  referred  to.*  He  made  it  by  heating  a  small 
quantity  of  "  PbCl2NH4Cl.H2O  "  with  water  in  a  sealed  tube. 

*  Bull.  Soc.  Chim.,  II,  xl,  15  (1883). 


ON  THE  AMMONIUM-LEAD  HALIDES. 


293 


It  is  evident  that  such  a  product  could  not  have  been  produced 
if  the  chlorides  had  not  contained  some  basic  substance. 

Experiments  with  Ammonium  Chloride  and  Lead  Iodide. 

Poggiale  *  and  Volkel  f  have  each  described  a  mixed  double 
halide  of  ammonium  and  lead,  neither  of  which  agrees  with 
the  types  of  unmixed  halides  which  we  have  described  in  this 
article.  Poggiale's  formula  is  PbI2.4NH4C1.2H2O,  while  Vol- 
kel's  is  PbI2.3NH4Cl.  It  is  evident  that  the  two  investigators 
obtained  the  same  compound,  for  both  made  their  products  in 
essentially  the  same  way,  and  both  describe  them  as  occurring 
in  the  form  of  silky  needles.  We  have  repeated  the  experi- 
ment of  dissolving  lead  iodide  in  ammonium  chloride  solutions 
and  have  readily  obtained  the  silky  crystals.  The  product 
resembles  exactly  the  salt  NH4PbI8.2H2O,  except  that  it  is 
considerably  paler  in  color  than  the  latter.  An  analysis  of  a 
pure  product,  carefully  dried  by  pressing  with  paper,  showed 
that  the  formulse  of  both  Poggiale  and  Volkel  are  incorrect, 
and  that  their  products  must  have  been  contaminated  with 
ammonium  chloride.  The  salt  corresponds  in  type  to  our 
double  iodide.  It  loses  one  molecule  of  water  on  exposure  to 
the  air  for  two  or  three  days,  becoming  much  darker  in  color ; 
the  second  molecule  of  water  goes  off  at  100° . 

Found. 

Ammonium   .     .     .  3.33 

Lead 34.83-34.68 

Chlorine    ....  5.11-  5.10 

Iodine 51.08-50.94 

Water  .  5.35 


Calculated  for 
NH4Cl.PbI2.2H,0. 

3.27 
37.60 

6.45 
46.14 

6.54 


The  analysis  indicates  that  the  lead  iodide  and  ammonium 
chloride  do  not  combine  quite  unchanged,  and  that  the  formula 
NH4Pb(Cl,I)3.2H2O  possibly  expresses  the  composition  of  the 
product  better  than  the  one  given  above.  In  the  course  of  our 
experiments  with  ammonium  chloride  and  lead  iodide,  we 
obtained  a  crop  of  crystals  which  showed  an  almost  complete 


*  Compt.  Rend.,  xx,  1180. 


t  Pogg.  Ann.,  Ixii,  252. 


294  ON  THE  AMMONIUM-LEAD  HALIDES. 

replacement  of  the  iodine  by  chlorine.  The  salt  was  a  1  :  2 
compound,  a  type  which  apparently  does  not  exist  among  the 
double  iodides  of  lead.  It  gave  the  following  analysis : 


Found. 


Calculated  for 


NH4Pb2Cl5. 

Ammonium 2.95 

Lead 66.82  67.93 

Chlorine 28.76  29.12 

Iodine 1.44  .  .  . 

The  view  that  certain  mixed  lead  double  halides  are  to  be 
considered  as  variable  mixtures  of  two  isomorphous,  unmixed 
double  halides  was  arrived  at  by  Wells  and  Wheeler  *  from 
experiments  with  caesium  chloride  and  lead  bromide.  Herty  f 
has  more  recently  arrived  at  the  same  conclusion  from  his 
investigation  of  the  mixed  double  bromide  and  iodide  of  potas- 
sium and  lead.  It  is  not  safe  to  conclude,  however,  because 
definite  mixed  double  halides  do  not  occur  in  some  cases,  that 
they  are  never  formed.  It  is  certain  that  there  is  a  tendency 
toward  the  formation  of  such  definite  compounds  in  many  cases. 
Tor  example,  it  is  to  be  noticed  that  in  the  above  analysis  of 
NH4Cl.PbI2.2H2O  there  is  only  a  slight  variation  from  the 
composition  required  by  the  formula,  while,  from  a  solution  of 
the  same  ingredients,  another  type  of  salt  was  deposited  which 
was  almost  free  from  iodine.  The  compound  Cs2HgCl2I2,  J 
described  by  one  of  us,  is  evidently  a  definite  mixed  double 
halide  which  is  not  intermediate  in  its  properties  between  the 
corresponding  chloride  and  iodide,  and  which  has  a  constant 
composition.  A  number  of  other  caesium-mercuric  halides 
were  described,  which  approached  a  constant  composition  when 
made  under  varying  conditions. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
March,  1893. 

*  Amer.  Jour.  Sci.,  Ixr,  129. 
t  Amer.  Chem.  Jour.,  xv,  81. 
I  Amer.  Jour.  Sci.,  xliv,  232. 


ON  THE   RUBIDIUM-LEAD   HALIDES,  AND  A 

SUMMARY  OF  THE  DOUBLE   HALIDES 

OF  LEAD.* 

BY  H.  L.  WELLS. 

THE  caesium-lead  and  potassium-lead  halides  have  already 
been  studied  in  this  laboratory,  and  an  account  of  the  ammo- 
nium compounds  is  given  in  the  preceding  article.  It  has 
therefore  seemed  desirable  to  make  an  investigation  of  the 
rubidium  salts  in  order  to  make  the  work  more  complete. 

2  :  1  Rubidium-Lead  Chloride,  2RbzPbCh.EzO. —  This  was 
formed  by  dissolving  lead  chloride  in  a  solution  of  rubidium 
chloride  which  was  so  concentrated  as  to  be  almost  saturated 
when  cold.  It  forms  colorless,  transparent,  slender,  flat  prisms 
which  retain  their  lustre  on  exposure  to  the  air.  Two  separate 
crops  were  analyzed. 

™rt  Calculated  for 

Pound.  2KbtPbCl4.H,0. 

Rubidium    .    .    .     29.63  29.85  32.39 

Lead 41.41  41.75  39.20 

Chlorine.     .    .     .    26.73  26.84  26.90 

Water     ....      2.29  2.01  1.51 

100.06  100.45  100.00 

The  amount  of  water  in  the  salt  seems  somewhat  uncertain, 
but,  since  there  was  no  evidence  of  loss  of  water  by  efflores- 
cence and  since  the  salt  was  simply  air-dried  without  being 
pulverized,  the  above  formula  is  preferred  to  Rb2PbCl4.H2O, 
which  requires  2.99  per  cent  of  water.  The  water  was  deter- 
mined by  heating  to  about  200° ;  at  100°  the  salt  lost  only 
about  one  quarter  of  its  water  in  twelve  hours. 

1:2  Rubidium-Lead  Chloride,  RbPb^Cl^.  —  This  com- 
pound forms  small,  prismatic  crystals  which  are  usually 

*  Amer.  Jour.  Sci.,  xlvi,  July,  1893. 


296  ON  THE  RUBIDIUM-LEAD  HALIDES. 

grouped  side  by  side  in  nearly  parallel  position.  It  is  pro- 
duced from  solutions  which  are  more  dilute  than  those  from 
which  the  preceding  salt  is  prepared,  and  it  is  formed  under 
rather  wide  limits  of  conditions.  Two  separate  crops  gave 
the  f oUowing  analyses :  Calculated  for 

Found-  EbPb2Cl6. 

Rubidium    .     .     .     13.09        12.68  12.63 

Lead 60.57        61.05  61.15 

Chlorine       .     .     .    26.19        26.29  26.22 

99.85      100.02  100.00 

2  :  1  Rubidium-Lead  Bromide,  ^Rb2PbBr4.H2  0.  —  This 
salt  resembles  the  corresponding  chloride,  both  in  its  formation 
and  appearance.  Two  crops  gave  the  following  analyses : 

_       ,  Calculated  for 

Found-  2Rb2PbBr4.H20. 

Kubidium    .     .     .     23.17        22.73  24.19 

Lead        ....     30.29        30.81  29.29 

Chlorine      45.04  45.26 

Water     ....      1.55          1.51  1.27 

100.09  100.00 

1  :  2  Rubidium-Lead  Bromide,  RbPb2Br5.  —  This  forms 
square  plates.  It  is  readily  prepared,  since  it  is  formed  under 
considerable  variations  of  conditions. 

w       ,  Calculated  for 

Found-  RbPb2Br6. 

Rubidium     .     .    .      9.81  9.50 

Lead 45.74  46.03 

Bromine  ....    44.62  44.47 

100.17  100.00 

111  Rubidium-Lead  Iodide,  RbPbIs.2H20.  —  This  is  the 
only  double  iodide  that  could  be  produced  under  widely  vary- 
ing conditions.  It  forms  very  slender,  hair-like  prisms  of  a 
pale  yellow  color.  It  rapidly  loses  its  water  when  exposed  to 
the  air,  undergoing  a  remarkable  change  of  color.  The  pale 
yellow  compound  quickly  assumes  an  orange  color,  then  the 
color  becomes  almost  like  that  of  the  original  salt.  It  is  evi- 
dent that  the  salt,  which  contains  two  molecules  of  water, 
loses  a  part  of  this,  probably  one  molecule,  with  change  of 
color  to  orange ;  then  the  remainder  of  the  water  is  lost  with 


ON  THE  RUBIDIUM-LEAD  HALIDES.  297 

another  change  of  color.  It  is  interesting  to  notice,  in  this 
connection,  that  the  salt  NH4PbClI2.2H2O  undergoes  a  similar 
change  of  color,  as  far  as  the  first  step  is  concerned,  on  losing 
one  molecule  of  water  when  it  is  exposed  to  the  air,  but  this 
salt  does  not  lose  its  second  molecule  at  ordinary  temperatures. 
A  sample  of  the  rubidium-lead  iodide  was  rapidly  pressed  on 
paper  until  some  of  the  particles  began  to  show  a  change  of 
color  to  orange.  Water  was  determined  in  this  sample  from 
the  loss  at  100°. 

•RVmnH  Calculated  for 

Found.  RbPbI8.2H20. 

Water 6.09  5.07 

An  air-dry  sample  gave  the  following  analysis : 

Pound.  Calculated. 

Kubidium     .    .     .    13.29  12.70 

Lead 28.95  30.73 

Iodine      ....     56.80  56.57 

99.04  100.00 

Summary. 

The  following  table  gives  a  list  of  the  lead  double  halides 
which  have  been  prepared  in  this  laboratory.  All  of  them 
were  new  compounds  except  KPbBr8.H2O  and  KPbI8.2H2O, 
these  having  been  previously  described  by  Remsen  and  Herty. 

4:1  2:1  1:1  1:2 

Cs4PbCl6        CsPbClg  CsPb2Cl6 

Cs4PbBr6        CsPbBr8  CsPb2Br6 

CsPbI3  

2Rb2PbCl4.H20      RbPb2Cl6 

2Rb2PbBr4.H2O     RbPb2Br6 

RbPbI8.2H20         

3KPbCl8.H20  KPb2Cl6 

K2PbBr4.I!20     3KPbBr8.H2O  KPb2BrB 

KPbBr8.H2O  

KPbI8.2H2O  

3NH4PbCl8.H20  NH4Pb2Cl5 

(NH4)2PbBr4.H20 NH4Pb2Br6 

NH4PbI8.2H20       

NH4PbClIa.?H80 


298  ON  THE  RUBIDIUM-LEAD  HALIDES. 

An  inspection  of  the  table  shows  that  the  caesium  salts  differ 
from  the  others  in  including  the  4  :  1  type  and  in  being  with- 
out any  2  :  1  salts.  It  is  quite  probable  that  we  have  not 
succeeded  in  preparing  all  the  salts  that  are  possible,  but  it 
seems  certain  that  the  4:1  rubidium,  potassium,  and  ammo- 
nium salts  cannot  be  made  on  account  of  the  comparative  in- 
solubility of  the  simple  halides.  The  caesium  salts  also  differ 
from  the  others  in  being  all  anhydrous.  The  hydrous  rubidium 
salts  have  less  water  or  lose  it  more  readily  than  the  potassium 
compounds.  KPbI8.2H2O  is  stable  in  the  air,  but  RbPbI8.2H2O 
loses  its  water  readily.  There  is  evidently  a  gradation,  in  af- 
finity for  water,  from  the  caesium  to  the  potassium  compounds. 
A  gradation  in  water,  from  the  chloride  to  the  iodide,  appar- 
ently exists  in  the  potassium  and  ammonium  compounds  of 
the  1 :  1  type.  That  such  gradations  in  water  exist  among 
the  double  halides,  increasing  with  the  atomic  weight  of  the 
halogens  and  decreasing  with  the  atomic  weight  of  the  alkali 
metals,  has  already  been  observed  by  Remsen.* 

The  simplicity  of  the  ratios  in  the  four  types  of  double  hal- 
ides of  lead  is  noticeable.  The  4  :  1  type,  according  to 
Werner's  remarkable  theory,  f  may  be  considered  as  the  ideal 
type  of  a  double  halide  of  an  alkali  metal  and  a  bivalent 
metal,  and  as  the  limit  beyond  which  the  ratios  of  alkali  metal 
to  lead  cannot  go.  The  type  is  represented,  as  Werner 
mentions,  by  numerous  double  cyanides  of  bivalent  metals, 
such  as  K4Fe(CN)6  and  by  other  salts,  such  as  K4CdCl6. 

The  number  of  2  :  1  lead  salts  that  we  have  prepared  is 
rather  small,  but  this  is  a  very  common  type  among  the  known 
double  halides  of  the  other  bivalent  metals. 

The  number  of  1  :  1  lead  salts  is  the  largest  of  all.  It  is 
remarkable  that  all  the  double  iodides  belong  to  this  type. 
This  is  also  a  well-known  type  of  bivalent  metal  double  hal- 
ides. It  is  noticeable  that  the  salt  CsPbBr3  is  dimorphous, 
while  three  mercuric  salts  of  the  same  type,  J  CsHgCl8, 
CsHgBr8,  and  CsHgClBr2  are  also  dimorphous. 

*  Amer.  Chem.  Jour.,  xir,  88.  f  Zeitschr.  anorg.  Chem.,  iii,  281. 

\  Amer.  Jour.  Sci.,  xliy,  222. 


ON  THE  RUBIDIUM-LEAD  HALIDES.  299 

The  1  :  2  salts  are  all  anhydrous,  and  a  chloride  and  bro- 
mide were  prepared  with  each  of  the  alkali  metals  and  with 
ammonium.  They  are  formed  under  wide  limits  of  condi- 
tions and  are  therefore  very  easily  prepared.  It  is  noticeable 
that  the  rubidium,  potassium,  and  ammonium  chlorides  of  this 
type  all  crystallize  in  prisms,  while  all  the  bromides  and  the 
chloride  containing  cassium  crystallize  in  plates.  A  number 
of  other  double  halides  of  this  type  are  known,  especially 
among  the  mercuric  compounds.  Herty  has  evidently  pre- 
pared a  potassium-lead  double  halide  of  the  1 :  2  type  contain- 
ing bromine  and  iodine,  although  he  interprets  his  results  in 
an  entirely  different  way.  In  a  recent  article  *  he  describes 
some  tabular  crystals  of  an  olive-green  color  which  he  has 
selected  and  analyzed  with  evident  care  and  skill.  He  gives 
the  following  analyses  of  three  separate  products : 

p.  95,  D  . 
p.  95,  E  . 
p.  104  . 

The  following  ratios  may  be  derived  from  the  above 
analyses : 

Pb       :        I  +  Br         :        K. 

p.  95,  D     .     .    .    2.  5.01  1.07 

p.  95,  E    ...    2.  5.15  1.08 

p.  104  ....    2.  5.08  1.08 

The  ratio  required  for  the  formula  KPb2(Br,I)6  is  Pb:  1  + 
Br :  K  =  2  :  5  :  1,  and  the  agreement  is  so  close  that  there  can 
be  no  doubt  that  this  is  the  formula.  Although  no  pure 
iodide  of  this  type  has  been  produced,  it  is  interesting  to 
notice  that  Herty's  compound  shows  that  the  potassium  salt 
is  capable  of  existence  when  mixed  with  a  relatively  large 
amount  of  the  bromide. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
March,  1893. 

*  Amer.  Chem.  Jour.,  xv,  pp.  94, 95,  97-99, 103, 104  (February,  1893). 


Pb. 

i. 

Br. 

K. 

44.89 

17.61 

32.59 

4.56  =  99.65 

45.42 

14.94 

34.72 

4.50  =  99.58 

43.87 

22.20 

29.03 

4.43  =  99.53 

ON  THE  DOUBLE  HALIDES  OF  ARSENIC  WITH 
CJESIUM  AND  KUBIDIUM;  AND  ON  SOME  COM- 
POUNDS OF  AESENIOUS  OXIDE  WITH  THE  HAL- 
IDES  OF  CAESIUM,  RUBIDIUM,  AND  POTASSIUM.* 

BY  H.  L.  WHEELER. 

No  compounds  of  arsenious  halides  with  alkaline  halides 
have  been  definitely  described.  Nickldsf,  in  his  work  on  the 
bromides  and  iodides  of  arsenic,  antimony,  and  bismuth,  states 
that  these  salts  combine  with  alkaline  bromides  and  iodides 
respectively,  but  in  the  case  of  arsenic  he  gives  no  analyses  of 
the  compounds  which  he  obtained,  and  he  does  not  describe 
the  methods  that  he  used  in  preparing  them.  He  does  not 
even  state  with  what  alkaline  halides  he  performed  his  experi- 
ments. Emmet,J  Harms,§  Schiff,  and  Sestini||  have  described 
compounds  of  arsenious  oxide  with  potassium  halides,  but  this 
class  of  bodies  has  been  most  thoroughly  studied  by  Riidorff.lT 
His  results  indicate  the  existence  of  two  types  of  this  class  of 
compounds,  the  first  containing  one  molecule  of  alkaline 
halide  to  one  of  arsenious  oxide,  the  other  having  these 
constituents  in  the  ratio  1:2.  In  the  present  investigation  a 
complete  series  of  the  caesium  and  rubidium  oxyhalides  of  the 
1 : 1  type  was  obtained,  while  the  formation  of  the  1 :  2  type 
was  not  observed.  There  is  evidently  a  gradation  in  stability 
from  the  oxychlorides  to  the  oxyiodides,  the  stability  increasing 
with  increasing  atomic  weight  of  the  halogens.  Attempts  to 
prepare  double  halides  of  pentavalent  arsenic  were  without 
success. 

*  Amer.  Jour.  Sci.,  xlvi,  August,  1893. 

t  Compt.  Rend.,  xlviii,  839 ;  Jour.  Pharra.,  Ill,  xli,  142 ;  Rep.  chim.  pure, 
i,366. 

t  Amer.  Jour.  Sci.,  I,  xviii,  58.  §  Ann.  Chem.  Pharm.,  xci,  371. 

II  Ibid.,  228,  72. 

T  Ber.  d.  Deutsch.  Chem.  Ges.,  xix.  2668 ;  Ibid.,  xxi,  3053. 


DOUBLE  HALIDES  OF  ARSENIC.  301 

The  new  compounds  to  be  described  in  this  article  are  the 
following : 

3CsC1.2AsCl8  3CsBr.2AsBr8  3CsI.2AsI8 

3BbC1.2AsCl,  3EbBr.2AsBr8  3RbI.2AsI8 

CsCl.As203  CsBr.As2O8  CsLAs208 

EbCl.Asa08  KbBr.As208  RbI.As208 

The  compound  As2O8.KI,  which  had  not  been  observed  by 
Riidorff,*  was  obtained  in  attempts  to  prepare  a  double  iodide 
of  potassium  and  arsenic. 

It  is  to  be  noticed  that  only  one  type  of  double  halides  was 
obtained.  This  type  corresponds  to  the  most  readily  prepared 
double  chloride  of  caesium  with  antimony,  described  by  Rem- 
sen  and  Saunders  f  and  of  caesium  and  bismuth,  described  by 
Remsen  and  Brigham.J  Many  attempts  were  made  to  prepare 
arsenic  double  halides  of  other  types  than  this  single  one,  but 
these  have  invariably  been  without  success,  although  several 
types  of  antimony  and  bismuth  double  halides  have  been 
described. 

It  has  been  shown  in  several  instances  by  Wells  and  Wheeler  § 
that  csesium  and  rubidium  halides  form  more  stable  or  more 
complete  series  of  double  salts  than  the  halides  of  the  other 
alkali  metals.  This  fact  is  again  well  illustrated  in  the  double 
halides  of  arsenic,  for  the  caesium  and  rubidium  double  halides 
are  prepared  without  difficulty,  while  with  potassium  no  double 
halides  were  obtained. 

Methods  of  Preparation. 

To  prepare  the  double  halides,  a  strong  acid  solution  is 
necessary,  in  order  to  prevent  the  decomposition  of  the  arseni- 
ous  halide  and  the  consequent  formation  of  oxy-compounds. 
The  double  halides  are  less  soluble  in  the  strong  than  in  the 
dilute  halogen  acids.  Excess  of  one  or  the  other  of  the  con- 
stituents has  no  effect  on  the  composition  of  the  products 

*  Loc.  cit.  t  Amer.  Chem.  Jour.,  xiv,  152. 

t  Ibid.,  p.  164.  §  Amer.  Jour.  Sci.,  Ill,  xliii,  475 ;  III,  xliv,  42. 


302  DOUBLE  HALIDES  OF  ARSENIC 

obtained.  The  formation  of  As2O8  compounds  was  observed 
on  treating  the  double  halides  or  a  solution  of  the  constituents 
in  strong  acids,  with  water  or  dilute  acids.  The  oxygen  com- 
pounds are  difficultly  soluble  in  dilute  acids;  strong  acids 
convert  the  caesium  and  rubidium  compounds  into  the  double 
halides. 

Method  of  Analysis. 

The  salts  were  filtered  on  the  pump,  and  without  delay  were 
carefully  freed  from  the  mother-liquor  by  pressing  on  paper. 
They  were  then  dried  in  the  air.  In  no  case  was  water  used 
to  wash  them.  In  order  to  determine  arsenic  the  salt  was  dis- 
solved in  the  cold  in  HC1  sp.  gr.  1.1,  and  hydrogen  sulphide 
passed  in  for  about  one  hour ;  then  a  little  alcohol  was  added, 
the  whole  was  warmed  on  the  water  bath  for  a  short  time,  in 
order  to  drive  off  the  excess  of  hydrogen  sulphide  and  effect 
the  separation  of  the  last  traces  of  arsenious  sulphide.  The 
sulphide  of  arsenic  was  collected  on  a  Gooch  filter,  and  after 
washing  with  water,  alcohol,  and  carbon  disulphide  it  was  dried 
at  100°  and  weighed.  Sulphuric  acid  was  added  to  the  filtrate, 
and  the  alkali  metal  determined  as  normal  sulphate  by  evapo- 
rating and  igniting  the  residue  in  a  stream  of  air  containing 
ammonia.  The  halogens  were  determined  in  a  separate  por- 
tion as  silver  halides  in  the  usual  manner. 

Caesium  and  Rubidium  Arsenious  Chlorides,  SCsCL^AsOl^ 
and  3KbCl.2AsClz. —  These  have  a  pale  yellow  color,  like  the 
corresponding  antimony  and  bismuth  double  chlorides.  The 
caesium  salt  was  obtained  by  dissolving  250  g.  of  CsCl  in 
dilute  HC1.  2  g.  of  As2O8  in  dilute  HC1  were  then  added. 
This  produced  a  precipitate  which  dissolved  on  the  addition 
of  about  2  liters  of  hot  HC1  sp.  gr.,  1.1.  On  cooling,  light 
yellow  crystals  were  deposited.  A  portion  of  these  was 
recrystallized  from  a  strong  HC1  solution  of  AsCl8.  The 
rubidium  salt  was  prepared  in  the  same  manner,  except  that 
much  stronger  solutions  were  required.  Saturated  solutions 
of  rubidium  and  arsenic  chlorides  in  20  per  cent  HC1  produce 
no  precipitate  on  mixing,  but  if  concentrated  HC1  is  added. 


WITH  CAESIUM  AND  RUBIDIUM. 


303 


brilliant  spangles  of  the  double  salt  separate.     The  analysis  of 
these  products  gave : 


Prepared  with  Ex- 
cess of  CsCl. 


Cs 46.14 

As 17.15 

Cl  36.89 


45.27 


36.74 


Found. 


Prepared  with  Ex- 
cess of  AsCl3. 

45.09 
17.11 
36.12 


Calculated  for 
3CsC1.2AsCls. 

45.94 
17.27 
36.79 


Kb 35.55 

As    .....     20.14 
Cl  44.04 


Calculated  for 
3RbC1.2AsCl8. 

35.33 
20.66 
44.01 


Both  salts  can  be  recrystallized  from  hydrochloric  acid  of 
sp.  gr.  1.1.  100  parts  of  HC1  sp.  gr.  1.2  dissolve  .429  parts  of 
the  caesium  salt  and  2.935  parts  of  the  rubidium  compound. 
Since  the  corresponding  potassium  salt  apparently  does  not 
exist,  these  solubilities  suggest  a  convenient  method  for  ob- 
taining caesium  and  rubidium  free  from  potassium. 

Ccesium  and  Rubidium  Arsenious  Bromides,  3CsBr.2AsBr^ 
and  3KbBr.£AsBry  —  These  are  amber-yellow,  the  shade 
being  somewhat  darker  than  that  of  the  chlorides.  They 
are  most  conveniently  prepared  by  using  an  excess  of  the 
alkaline  halide.  Strong  hot  solutions  of  the  alkaline  bro- 
mides were  made  in  about  40  per  cent  HBr.  On  adding 
crystals  of  AsBr3  these  melted,  but  soon  solidified  to  a  yellow 
mass  of  the  double  halide.  This  dissolved  on  boiling,  and,  on 
cooling,  brilliant  yellow  crystals  were  obtained.  These  com- 
pounds can  be  recrystallized  unaltered  from  strong  HBr. 
Analysis  gave : 


Cs    .    .    .    . 

Pound. 

.     .     .    31.91 

Calculated  for 
3CsBr.2AsBr8. 

31.44 

As    .     .    .    . 

.    .     .    11.89 

11.82 

Br 

56.94 

56.74 

Prepared  with  Ex-    Prepared  with  Ex- 
cess of  RbBr.  cess  of  AsBr3. 


Kb 
As 
Br 


23.35 
12.55 
63.97 


64.43 


Calculated  for 
3RbBr.2AsBr,. 

22.77 
13.31 
63.92 


304  DOUBLE  HALIDES   OF  ARSENIC 

Ccesium  and  Rubidium  Arsenious  Iodides,  3CsI.2AsIz  and 
3RbI.2AsIy  —  These  are  deep  red,  the  larger  crystals  of  the 
csesium  compound  are  more  opaque  and  appear  black.  To 
prepare  these  compounds  the  normal  alkaline  iodides  were  dis- 
solved in  strong  colorless  hydriodic  acid,  and  these  solutions 
were  then  saturated  boiling  with  crystals  of  Asia.  Unless  the 
hydriodic  acid  is  decolorized  the  product  obtained  in  the  case 
of  the  csesium  salt  is  generally  impure,  being  mixed  with 
CsI3.* 

A  well-crystallized  product  of  the  double  csesium  salt  was 
obtained  by  preparing  the  salt  in  the  presence  of  considerable 
alcohol.  Analysis  of  these  compounds  gave 

,,       ,        Calculated  for  ipnv,nA  Calculated  for 

Found.          3C8I.2A8l8.  3RbI.2AsI8. 

Cs    .    .     24.38       23.58  Kb    .     .    16.86     .  .  .       16.55 

As    .    .      8.92         8.87  As     .     .      9.96    10.60        9.68 

I  ...    67.23       67.55  I  ...     73.65     .  .  .       73.77 

An  attempt  was  made  to  prepare  potassium  arsenious  chlo- 
ride by  mixing  solutions  of  potassium  chloride  and  arsenious 
acid,  saturated  solutions  of  these  substances  in  concentrated 
HC1  being  used  for  the  purpose.  No  precipitate  was  thus 
produced,  and,  on  concentrating  the  solution,  potassium  chlo- 
ride was  deposited.  Aqueous  solutions  of  potassium  chloride, 
when  added  to  solutions  of  arsenic  trioxide  in  concentrated 
HC1,  gave  precipitates  consisting  chiefly  of  As2O8.  Analogous 
experiments  with  potassium  bromide  and  arsenious  bromide 
gave  similar  results,  and  operating  in  the  same  way  with  KI 
and  AsI3  in  concentrated  HI  solutions,  nothing  but  crystals  of 
AsI8  or  mixed  crops  of  AsI3  and  KI  were  obtained.  Similar 
negative  results,  in  respect  to  the  formation  of  double  halides 
of  ammonium  and  arsenic,  have  been  obtained  by  Wallace,  f 

Compounds  of  Arsenic  Trioxide  with  Alkaline  Halides^ 
Cs  Cl.As2  03  and  Mb  Cl.Asz  Os.  —  When  a  hot  saturated  aqueous 
solution  of  25  g.  of  csesium  chloride  was  saturated  with 
3CsC1.2AsCl8,  a  finely  divided  white  precipitate  was  formed  on 

*  Am.  Jour.  Sci.,  xliii,  17  ;  Zeitschr.  anorg.  Chem.,  i,  85. 
t  Phil.  Mag.,  IV,  xvi,  358;  xvii,  122,  261. 


WITH  CAESIUM  AND  RUBIDIUM.  305 

cooling  (analysis  1).  When  6.5  g.  of  the  double  chloride 
were  dissolved  in  800  c.  c.  of  a  cold-saturated  solution  of  As8O3 
in  HC1  sp.  gr.  1.1  by  the  aid  of  heat,  a  similar  precipitate 
was  obtained  (analysis  2).  Products  intermediate  in  composi- 
tion were  obtained  by  recrystallizing  the  double  halide  from 
water  (analysis  3),  from  10  per  cent  HC1  (analysis  4),  and 
from  15  per  cent  HC1  (analysis  5). 


Cs  .     .    .  41.51  41.85    41.75  41.80            25.56  34.29 

As  ...  35.59  34.58    35.37  .  .  .             47.64  43.05 

Cl .  .     .     .  11.46     .  .  .      11.31  .  .  .             11.64  8.86 

O  .  .    .    .  [11.44]  .  .  .    [11.57]  .  .  .  [15.16]  [13.80] 


Cs  

4. 

35.30 

5. 

33.92 

uaicmaiea  101 
CsCl.As2Os. 

36.29 

As  

39.14 

38.10 

40.93 

Cl   

10.63 

11.42 

9.68 

0    

[14.93] 

[16.56] 

[13.10] 

The  analyses  show  a  considerable  variation  from  the  com- 
position required  by  the  formula,  the  products  made  under  the 
extreme  conditions  giving  ratios  of  arsenious  oxide  to  caesium 
chloride  of  3  :  4  and  3  :  2  instead  of  1:1.  The  conditions 
varied  so  widely,  however,  that  it  seems  fair  to  assume  the 
existence  of  a  1  :  1  compound. 

When  the  double  chloride  of  rubidium  was  recrystallized 
from  about  15  per  cent  HC1,  a  white  crystalline  crust  was 
obtained  on  slowly  cooling.  This  gave  analytical  results 
agreeing  with  the  formula  RbCl.As2O8. 

Calculated  for 


Rb      ......    26.90  26.80 

As  ..........  47.03 

Cl  .......    11.41  11.13 

O    ..........  15.04 

Under  the  microscope  these  compounds  appear  as  irregular 
grains  or  plates,  of  indefinite  crystalline  form. 


306 


DOUBLE  HALIDES  OF  ARSENIC 


OsBr.A82Os  and  RbBr.AszOz.  —  WheD  the  double  bromides 
are  recrystallized  from  water,  or  dilute  HBr,  they  yield  these 
oxy-compounds,  and  these  generally  separate  in  the  form  of  a 
white  crust  on  the  bottom  and  sides  of  the  beaker.  Analysis 
of  such  products  gave : 


Cs    .    . 

3CsBr.2AsBr. 
recrystallized 
from  Water. 

.    .     .      32.42 

3CsBr.2AsBr. 

recrystallized 
from  CsBr 
Solution. 

Calculated  for 
CsBr.AsjOg. 

32.36 

As   .    . 

.     .     .      36.52 

36.50 

Br   . 

.     .     .       1957 

19.59 

19.46 

O 

ni.491 

11.68 

LbBr.2AsBr8 
rom  Water. 

Calculated  for 
EbBr.A62O8. 

16.56 

23.52 

50.74 

41.27 

15.91 

22.01 

[16.79] 

13.20 

3RbBr.2AsBrs 
from  dilute  HBr. 

Rb 24.24 

As 40.06 

Br 24.53 

O 11-17 


It  is  to  be  noticed  that  the  product  obtained  by  recrystal- 
lizing  3RbBr.2AsBr8  from  water  is  impure,  while  the  caesium 
compound  made  in  the  same  way  corresponds  to  the  formula. 
This  is  an  illustration  of  the  greater  tendency  of  the  caesium 
halide  to  form  double  salts  than  in  the  case  of  the  rubidium 
halide.  Both  these  compounds  are  white,  but  the  rubidium 
compound  turns  somewhat  yellow  on  drying.  Under  the 
microscope,  six-sided  plates  were  seen  in  the  case  of  the 
caesium  compound  when  the  solution  was  slowly  cooled. 
There  were  also  observed  hexagonal  crystals  with  a  short 
columnar  rhombohedral  habit.  They  were  uniaxial  with 
weak,  negative  double  refraction.  The  rubidium  compound 
was  also  obtained  in  hexagonal  crystals  showing  rhombohedral 
symmetry  and  weak  negative  double  refraction. 

CsI.AstOs,  RbI.As2Os  and  KI.As2Os.  —  The  formation  of 
these  compounds  was  observed  when  dilute  hydriodic  acid 
solutions  of  the  alkaline  iodides  were  mixed  with  dilute 
acid  solutions  of  AsI8.  If  the  solutions  are  mixed  while  hot, 
these  double  salts  separated  on  cooling  in  the  form  of  crystal- 


OF  THE 


UNIVERSITY 

OF          ,. 

41    ICO 


WITH  CAESIUM  AND  RUBIDIUM. 


307 


line  yellow  crusts  on  the  bottom  and  sides  of  the  beaker. 
These  crystals  are  generally  somewhat  larger  than  those  of 
the  compounds  of  As2O3  with  the  chlorides  and  bromides. 
Under  the  microscope  they  exhibited  the  form  of  six-sided 
plates.  These  show  a  strong  negative  double  refraction. 

The  potassium  compound  also  appeared  in  the  form  of  six- 
sided  plates ;  these  remained  dark  when  rotated  between 
crossed  nicols.  They  were  too  small  to  afford  an  axial  figure, 
as  the  largest  plates  did  not  exceed  0.01  mm.  in  diameter. 
They  are  probably  hexagonal.  Analyis  gave : 

Wnimrt  Calculated  for 

Found.  CsI.Aa,0,. 

Cs 29.31  29.04 

As 32.01  32.75 

I 28.94  27.73 

0 [9.74]  10.48 

Calculated  for 
RbI.As2O8. 

Kb 20.35  20.83 

As 36.78  36.54 

I 31.94  30.93 

0 [10.93]  11.70 

Calculated  for 
KI.AsjjOa. 

K 10.75  10.74 

As 42.85  41.20 

I 34.13  34.88 

0 [12.27]  13.18 

Crystallography. 

The  crystallization  of  the  caesium  and  rubidium  arsenious 
halides  is  hexagonal.  They  were  all  measured  and  found 
to  be  isomorphous.  In  general  the  habit  was  holohedral, 
although  in  the  case  of  caesium  arsenious  bromide  it  is  rhom- 
bohedral.  All  these  salts  show  a  pronounced  basal  cleavage, 
and  plates  parallel  to  this,  examined  with  the  stauroscope,  are 
uniaxial:  the  double  chlorides  and  bromides  show  a  weak 
negative  double  refraction,  while  the  double  iodides  are  posi- 
tive. The  forms  observed  are  as  follows: 


308 


DOUBLE  HALIDES   OF  ARSENIC 


c  0001  0 
a  1150  i-2 
m  10TO  / 


r          10T1  1 

z          01T1        -1 
p          2021          2 


The  steep  pyramid  p  was  found  only  on  the  iodides. 
The  following  table  gives  the  lengths  of  the  vertical  axes 


3CsC1.2AsCl8 

3KbC1.2AsCl8 

3CsBr.2AsBr8 

3RbBr.2AsBr8 

3CsI.2AsIs8 

3BbI.2AsI,  . 


1.209 
1.210 
1.219 
1.220 
1.244 
1.243 


1. 


A  comparison  of  the  above  axial  ratios  shows  the  interest- 
ing fact  that  the  substitution  of  rubidium  for  caesium  produces 
no  appreciable  effect  hi  the  lengths  of  the  axes,  and  that  in 
this  series  the  vertical  axes  lengthen  as  the  atomic  weight  of 
the  halogens  increases.  The  crystals  were  sufficiently  stable 
to  yield  good  measurements,  although  on  long  exposure  they 
usually  lose  their  lustre.  In  the  lists  of 
measurements  the  angles  chosen  as  fun- 
damental are  noted  by  an  asterisk. 

3CsCl.2AsCls.  —  This  salt  was  made 
hi  crystals  about  1-2  mm.  in  diameter. 
The  forms  observed  are  w,  a,  r,  2,  and 
c.     A  careful  search  was  made,  for  indi- 
cations of  a  rhombohedral  development 
of    the  faces  r  and  2,   but  none    was 
found.      Apparently    they  are    always   holohedral   in    their 
development,  Fig.  1. 


m 


MAC,  10TOA0001 
c  A  r,  0001  A  10T1 
r  AW,  11T1  A  1010 
m  A  z,  10TO  A  01T1 
r  A  «,  10T1  A  01T1 


Measured. 
90° 

*54°  24' 
35°  39' 
66°  3' 
47°  53' 


Calculated. 
90° 

35°  36' 

66°    V 

47°  58' 


There  is  a  rather  poor  prismatic  cleavage,  and  plates  parallel 
to  this  show  parallel  extinction. 


WITH  CAESIUM  AND  RUBIDIUM. 


3RbCl.%AsClz.  —  This  salt  was  made 
in  crystals  up  to  about  5  mm.  in  diameter. 
The  forms  observed  are  <?,  m,  r,  and  2. 
The  faces  r  and  2  were  seldom  present, 
but  when  these  did  occur  it  could  not  be 
seen  whether  they  exhibited  rhombohe- 
dral  symmetry  or  not.  Penetration  twins 
are  common,  the  twinning  plane  being 
the  rhombohedron  0111,  Fig.  2. 

Measured. 

c  A  c  (twin),  0001  A  0001  *71°  3' 
c  AT-,  0001  A  1011  54°  21' 
m  A  r,  10TO  A  1011  35°  39' 


Calculated. 


64° 

35° 


On  examining  this  salt  in  convergent  polarized  light  a  uni- 
axial  cross  is  seen  whose  arms  are  not  black  but  a  deep  and 
brilliant  blue,  the  character  being  negative.  When  examined 
in  monochromatic  red  light,  the  crystals  are  nearly  isotropic, 
the  double  refraction  being  extremely  weak  and  probably 
negative.  In  blue  light,  however,  a  distinct  cross  is  seen 
accompanied  by  axial  rings.  This  difference  between  red  and 
blue  explains  the  colored  cross  seen  in  white  light.  Sections 
parallel  to  the  axis  c  show  the  deep  peculiar  blue  charac- 
teristic of  uniaxial  bodies  with  the  above-mentioned  optical 
properties. 


3CsBr.%AsBrz.  —  This  salt   was   made  in   crystals  up    to 
mm.  in  diameter.     The  forms  observed  are  <?,  w,  r,  and  2. 


310 


DOUBLE  HALIDES  OF  ARSENIC 


This  is  the  only  salt  of  the  series  that  has  a  rhombohedral 
habit,  and  as  the  angle  of  the  rhombohedron  is  nearly  90°  the 
crystals  look  like  cubes.  Fig.  3  shows  an  ideal  combination 
of  r  with  m,  2,  and  c.  This  form  was  not  observed,  as  the 
crystals  are  invariably  twins.  An  ideal  representation  of  the 
twinning  is  given  in  Fig.  4.  The  r  faces  were  so  curved 
and  striated  that  no  exact  measurements  could  be  made  from 
them. 

Measured.  Calculated. 

m  A  «,  01TO  A  01T1     *35°  23' 

»  AZ,  10T1  A  T101       ...      89°  50' 


z.  —  This  salt  was  made  in  small  crystals,  up 
to  2  mm.  in  diameter.  The  forms  observed  were  <?,  w,  and  r. 
The  crystals  were  made  in  two  habits.  When  prepared  with 
an  excess  of  RbBr,  it  separates  in  prismatic  crystals  which 
resemble  the  form  of  caesium  arsenious  chloride,  Fig.  1.  In 
one  experiment,  by  using  an  excess  of  AsBr3,  contact  twins 
were  obtained.  Here  the  twinning  plane  is  the  unit  rhombo- 
hedron, as  in  Fig.  2,  but  some  of  the  faces  are  lengthened  par- 
allel to  the  edge  between  the  two  basal  planes  (Fig.  5). 


c  AC  (twin),  0001  A  0001 
c  AT,  0001  A  10T1 
r  A  m,  1011  A  10TO 
r  A»,  lOllAOlTl 
m  A  *  10TO  A  01T1 


Measured. 


70C 
54C 
*35C 
48C 
65C 


Calculated. 

70°  44' 


WITH  CAESIUM  AND  RUBIDIUM.  311 

3CsI.%AsIz.  —  This  salt  was  made  in  beautiful  crystals  up  to 
3  mm.  in  length.  The  forms  observed  are  p  and  <?.  The  habit 
is  that  of  a  steep  doubly  terminated  hexagonal  pyramid,  with 
the  basal  planes  small  or  wanting.  Often  the  middle  edges 
are  rounded  by  oscillatory  combinations  of  the  pyramids  giv- 
ing rise  to  horizontal  striations.  There  was  no  indication  of  a 
prism  or  of  a  rhombohedral  development  of  the  pyramidal 
faces. 

Measured.  Calculated. 

c*p,  0001  A  2021  *70°  49' 

p  AJP,  2021  A  2021  38°  19'  38°  22' 

p  Ajp,  2021  A  0221  56°  24J'          56°  21'  34" 

This  salt  is  without  optical  anomalies,  and  no  pleochroism 
was  observed. 

3RbI.£AsI3.  —  This  salt  was  prepared  in  very  small  crystals, 
not  over  1  mm.  in  length.  The  forms  observed  were  c,  w,  and 
p.  The  habit  is  similar  to  Fig.  6,  but  usually  the  middle  edges 
are  replaced  by  the  faces  of  the  prism  m  or  are  rounded  by 
horizontal  striations. 

Measured.  Calculated. 

p  A  p,  2021  A  0221  *56°  21' 

c  A  p,  0001  A  2021  70°  47'  70° 

p  A  m,  2021  A  10TO  19°  12'  20°  56' 

Optically  this  salt  shows  anomalies.  Basal  cleavage  plates 
between  crossed  nicols  are  not  dark,  but  light  and  remain  so 
during  revolution.  In  convergent  light  the  locus  of  an  optic 
axis  is  seen  in  the  centre  of  the  field  coinciding  with  the  ver- 
tical axis  <?.  The  bisectrix  lying  nearest  this  axis  is  that  of 
least  elasticity,  C.  The  salt  is  not,  however,  properly  biaxial ; 
the  plane  of  the  optic  axes  is  sometimes  parallel,  sometimes 
perpendicular  to  the  edge  of  the  prism.  Moreover  this  direc- 
tion often  changes  from  place  to  place  in  the  same  plate,  and 
at  times  no  bar  is  seen,  but  a  black  dot  in  the  centre  of  the 
field  surrounded  by  rings.  Such  behavior  can  be  explained  by 
supposing  the  crystal  to  be  in  a  condition  of  internal  strain. 
Sections  parallel  to  the  prism  sometimes  remain  light  between 
crossed  nicols,  sometimes  extinguish  at  varying  angles  and 


312  DOUBLE  HALIDES  OF  ARSENIC. 

show  a  slight  pleochroism,  the  absorption  being  e  >  «o;  the 
color  a  deep  reddish  orange. 

In  conclusion  the  author  wishes  to  express  his  indebtedness 
to  Prof.  H.  L.  Wells  for  valuable  advice  in  connection  with 
the  present  investigation,  and  to  Prof.  S.  L.  Penfield,  under 
whose  direction  the  crystallography  of  these  salts  was  investi- 
gated. The  author  is  also  indebted  to  Mr.  L.  V.  Pirsson  for 
aid  in  the  optical  description  of  these  salts. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
March,  1893. 


ON  SOME  DOUBLE   SALTS   OF  LEAD 
TETRACHLORIDE.* 

BY  H.   L.   WELLS. 

THE  existence  of  lead  tetrachloride  has  long  been  surmised 
from  the  fact  that  the  corresponding  oxide,  when  dissolved  in 
cold  hydrochloric  acid,  gives  a  yellow  solution  in  which  sul- 
phuric acid  does  not  give  an  immediate  precipitate.  Lead 
tetrachloride  itself,  however,  has  never  been  isolated,  nor  has 
any  double  salt  which  it  forms  been  satisfactorily  described. 

Sobrero  and  Selmi  f  found  that  when  chlorine  is  passed  into 
a  solution  containing  sodium  chloride  and  lead  chloride,  the 
liquid  becomes  yellow.  They  found  it  impossible  to  isolate 
the  compound  either  by  evaporation  or  cooling,  so  that  they 
determined  the  lead,  sodium,  and  chlorine  in  such  a  solution, 
and  found  it  to  contain  these  constituents  in  the  ratio  corre- 
sponding to  PbCl4  +  9NaCl.  Sobrero  and  Selmi  say  that  per- 
haps this  is  the  formula  of  the  compound,  but  they  put  a 
question-mark  after  it.  Their  analysis  indicates  the  existence 
of  PbCl4  in  combination  with  NaCl,  but  if  the  solution  had 
contained  a  compound  of  that  composition,  which  was  stable 
with  water,  it  probably  could  have  been  isolated  by  evapora- 
tion. The  fact  is  that  the  double  salts  of  lead  tetrachloride  are 
not  stable  with  water,  as  will  be  shown  in  the  present  article. 
Therefore,  since  a  large  excess  of  sodium  chloride  must  have 
been  present  in  the  solution  of  Sobrero  and  Selmi,  their  analy- 
sis could  not  have  determined  the  composition  of  the  double 
salt  that  it  contained. 

Nickles*  saturated  a  strong  solution  of  calcium  chloride  with 
lead  chloride  and  chlorine  and  analyzed  the  solution.  He 

*  Amer.  Jour.  ScL,  xlvi,  September,  1893. 
t  Ann.  Chim.  Phys.,  Ill,  xxix,  161. 

*  Ibid.,  IV,  x,  323. 


314  ON  SOME  DOUBLE  SALTS 

found  it  to  contain  lead,  calcium,  and  chlorine  in  the  propor- 
tions represented  by  PbCl4  +  16CaCl2.  In  conclusion  NicklSs 
does  not  claim  that  any  such  double  salt  exists,  but  merely 
claims  to  have  indicated  the  existence  of  PbCl4. 

In  view  of  the  fact  that  the  formulae  PbCl4  +  9NaCl  and 
PbCl4  -f  16CaCl2  merely  represented  the  composition  of  solu- 
tions, it  is  remarkable  that  they  are  given  in  some  handbooks 
of  chemistry  as  real  chemical  compounds.  It  may  be  men- 
tioned that  Carnegie*  has  used  the  formula  PbCl4.9NaCl  in 
support  of  a  theory  on  double  halides. 

O.  Seidel  f  mentions  unsuccessful  attempts  to  isolate  PbCl4 
and  its  double  salts  with  the  chlorides  of  other  metals. 

Fisher  J  dissolved  lead  peroxide  in  hydrochloric  acid,  and 
found  that  all  the  lead  in  the  solution  was  precipitated  again 
as  peroxide  by  the  addition  of  sodium  acetate.  He  was  evi- 
dently not  aware  of  the  fact  that  Rivot,  Beudant,  and  Daguin  § 
had  shown,  long  before,  that  lead  is  completely  precipitated  as 
peroxide  by  the  addition  of  sodium  acetate  and  chlorine  to  its 
solutions.  Fisher  found  that  two  atoms  of  chlorine  were  used 
(as  would  be  expected)  in  precipitating  one  atom  of  lead  as 
peroxide.  His  conclusion  that  his  experiments  showed  the 
existence  of  lead  tetrachloride  has,  apparently,  little  foundation. 

More  recently,  Ditte  ||  has  made  some  experiments  on  the 
solubility  of  lead  chloride  in  solutions  containing  hydrochloric 
acid  and  chlorine.  He  apparently  does  not  believe  in  the 
existence  of  lead  tetrachloride,  for  he  does  not  mention  the 
compound,  while  he  explains  the  precipitation  of  lead  peroxide, 
when  such  solutions  are  diluted,  by  saying  that  lead  chloride 
is  partly  dissociated  by  the  act  of  solution,  that  the  solution 
then  contains  oxide  of  lead,  and  that  this  is  peroxidized  by  the 
oxides  of  chlorine  formed  when  chlorine  is  passed  into  the 
solution. 

Nikolukine  has  succeeded  in  isolating  double  salts  of  lead 
tetrachloride  with  ammonium  and  potassium  chlorides.  He 

*  Am.  Chem.  Jour.,  xv,  10, 1893.  t  Jour.  pr.  Ch.,  II,  xx,  205,  1879. 

t  Jour.  Chem.  Soc.,  xxxv,  282,  1879.          §  Ann.  Mines,  V,  iv,  239,  1853. 
||  Ann.  Chim.  Phys.,  V,  xxii,  566,  1881. 


OF  LEAD   TETRACHLORIDE.  315 

showed  that  these  compounds  contain  lead  and  extra  chlorine 
in  the  proportion  required  for  PbCl4,  but  there  is  no  evidence 
in  the  abstracts  of  mYarticle  *  that  he  determined  the  composi- 
tion of  the  double  salts.  His  original  article  in  Russian  is  not 
accessible  to  me.  Nikolukine  prepared  the  compounds  by 
dissolving  lead  dioxide  in  concentrated  hydrochloric  acid  in 
sealed  tubes,  and  adding  the  alkaline  chlorides  to  the  solutions 
thus  produced.  He  describes  the  double  salts  as  having  a 
lemon-yellow  color,  and  states  that  they  are  pretty  stable,  the 
ammonium  chloride  compound  being  decomposed  at  120°. 

The  present  investigation  has  been  undertaken  with  the  view 
of  determining  the  composition  of  the  salts  which  Nikolukine 
discovered,  and  especially  in  order  to  investigate  the  corre- 
sponding rubidium  and  caesium  compounds,  which,  from  anal- 
ogy, were  expected  to  be  more  insoluble  and  stable  than  the 
potassium  salt.  As  a  result,  it  has  been  found  possible  to  pre- 
pare the  whole  series  in  a  state  of  purity,  and  the  expectations 
in  regard  to  the  easy  preparation  of  the  rubidium  and  caesium 
salts  have  been  fully  realized.  The  following  salts  are  to  be 
described : 

(NH4)aPbCl, 

K2PbCl6 

Eb2PbCl6 

Cs2PbCl6 

These  salts  are  all  yellow,  and  they  all  crystallize  in  the 
isometric  system  with  an  octahedral  habit. 

These  salts  show  a  new  relation  between  lead  and  other 
metals  of  Mendele'eff's  group  IV,  with  which  this  type  is  very 
common,  especially  among  the  double  fluorides.  It  is  to  be 
noticed  also  that  this  type  is  almost  invariable  among  the 
double  salts  which  tetrahalides  form,  for  platinum,  iridium, 
osmium,  and  palladium  give  analogous,  isomorphous  com- 
pounds, while,  as  has  been  recently  shown  by  Dr.  H.  L. 
Wheeler  of  this  laboratory,  tellurium  gives  an  extensive  series 
of  octahedral  salts  of  this  type.  The  octahedral  form  of  the 

*  Berichte,  xviii,  370.  1885 ;  Jour.  Chem.  Soc.,  i,  123. 


316  ON  SOME  DOUBLE  SALTS 

anhydrous  salts  of  this  type  is  very  characteristic,  and  it  seems 
to  be  universal,  except  among  the  fluorides. 

All  of  the  lead  salts  to  be  described  are  decomposed  by  water 
with  the  formation  of  lead  peroxide.  Chlorine  is  usually  set 
free  at  the  same  time.  It  may  be  assumed  that  two  successive 
reactions  take  place,  which  may  be  represented  by  the  following 
equations : 

(1)  PbCl4  +  2H20  =  Pb02  +  4HC1 

(3)  Pb02  +  4HC1  =  PbCl2  +  C12  +  2H20 

The  extent  to  which  the  second  reaction  takes  place  depends 
upon  the  dilution  and  the  temperature.  If  the  amount  of 
water  present  is  not  too  great,  a  state  of  equilibrium  is  reached 
when  a  sufficient  amount  of  alkaline  chloride,  hydrochloric 
acid,  and  chlorine  have  gone  into  solution,  and  the  decomposi- 
tion stops.  The  caesium  salt  is  more  slowly  decomposed  by 
water  than  others.  All  the  salts  are  decomposed  by  boiling 
with  an  excess  of  hydrochloric  acid,  but  the  decomposition  of 
the  caesium  compound  is  remarkably  slow,  especially  in  solu- 
tions containing  much  csesium  chloride. 

When  free  chlorine  is  present  the  csesium  salt  is  almost 
completely  insoluble  in  strong  solutions  of  csesium  chloride  and 
in  hydrochloric  acid.  Although  the  rubidium  salt  is  consider- 
ably more  soluble,  the  difference  is  not  great  enough  so  that  a 
quantitative  separation  can  be  made.  It  will  be  shown  in  the 
following  article  that  caesium  can  be  approximately  separated 
from  potassium,  sodium,  and  lithium  by  this  means,  and  that 
when  rubidium  is  also  present  the  csesium  can  be  approxi- 
mately determined  indirectly. 

The  salts  to  be  described  can  be  washed  with  hydrochloric 
acid  containing  chlorine.  They  are  perfectly  stable  on  expo- 
sure to  the  air.  When  heated  in  capillary  tubes,  the  ammonium 
salt  begins  to  whiten  at  about  225°,  the  potassium  salt  at  about 
190°,  and  the  csesium  and  rubidium  salts  at  about  280°.  This 
temperature  for  the  decomposition  of  the  ammonium  salt  is 
about  100°  higher  than  that  given  by  Nikolukine.  It  is  prob- 
able that  difference  is  due  to  a  typographical  error. 


OF  LEAD   TETRACHLORIDE.  317 

Attempts  were  made  to  prepare  corresponding  sodium  and 
calcium  salts,  without  success. 

In  analyzing  the  salts,  lead  was  separated  and  weighed  as 
sulphate,  and,  in  the  filtrate  from  this,  the  alkali  metal  was 
determined  as  sulphate.  To  determine  chlorine,  a  separate 
portion  was  decomposed  by  a  solution  of  sodium  arsenite  and 
chlorine  was  determined  in  this  as  usual. 

Ammonium-Plumbic  Chloride,  (NH^)zPbCl&.  —  In  prepar- 
ing this  salt,  Nikolukine's  method  of  using  sealed  tubes  was 
found  to  be  unnecessary.  A  solution  of  lead  tetrachloride  was 
made  by  adding  slightly  diluted  hydrochloric  acid  to  an  excess 
of  lead  dioxide  at  0°.  This  solution  was  quickly  filtered 
through  asbestos,  and  a  saturated,  cold  solution  of  ammonium 
chloride  in  dilute  hydrochloric  acid  was  added  until  an  abun- 
dant, yellow,  crystalline  precipitate  was  produced.  The  salt 
was  pressed  on  paper,  and  then  air-dried. 

v~  *A  Calculated  for 

(NH4)2PbCl«. 

Ammonium 7.90 

Lead 44.61  45.39 

Chlorine 46.53  45.71 


Potassium-Plumbic  Chloride,  K2PbCl6.  —  Chlorine  was 
passed  into  a  solution  saturated  with  potassium  chloride,  lead 
chloride,  and  hydrochloric  acid  at  0°,  without  producing  the 
double  salt.  Nikolukine  has  stated  that  the  salt  is  soluble  in 
an  excess  of  potassium  chloride,  and,  acting  upon  this  sugges- 
tion, another  solution  was  made,  like  the  former  except  that 
no  potassium  chloride  was  used.  On  mixing  about  equal  vol- 
umes of  the  two  solutions  and  letting  the  mixture  stand  at  0° 
for  several  hours,  a  well-crystallized  crop  of  the  yellow  double- 
salt  was  obtained.  The  air-dry  salt  was  analyzed. 

Found.  Cal™££d£or 

Potassium 15.30 

Lead 41.91 

Chlorine 42.49 

9070 
Loss  on  heating  ....    15.07       C12    14.25 


318  ON  SOME  DOUBLE  SALTS 

The  above  method  of  preparation  gives  a  small  yield,  and  it 
would  probably  be  better  to  use  a  method  analogous  to  that  by 
which  the  ammonium  salt  was  prepared. 

Rubidium-Plumbic  Chloride,  Rb2PbCl6.  —  When  65  g.  of 
rubidium  chloride  were  dissolved  in  250  c.  c.  of  water  with 
4  g.  of  lead  chloride,  no  precipitate  was  produced  by  saturating 
the  solution  with  chlorine,  but,  on  adding  an  equal  volume  of 
concentrated  hydrochloric  acid  to  this  solution,  an  abundant, 
yellow,  crystalline  precipitate  was  produced.  This  was  col- 
lected on  a  filter,  washed  with  hydrochloric  acid  containing 
chlorine,  and  air-dried. 

Wrt  ,„  j  Calculated  for 


Rubidium  ......    28.62  28.93 

Lead      .......     34.98  35.03 

Chlorine    ......    35.85  36.03 

9045  100.00 

Loss  on  heating  ....    12.41  C12    12.01 

A  solution  35  c.  c.  in  volume,  made  of  equal  volumes  of 
concentrated  hydrochloric  acid  and  water,  and  containing 
.0619  g.  of  rubidium  and  double  the  theoretical  quantity  of 
lead  chloride,  was  saturated  with  chlorine.  A  precipitate  of 
the  double  salt  was  produced,  which,  after  standing  several 
hours,  was  collected  upon  a  Gooch  filter.  The  rubidium  in 
this  precipitate  was  determined  and  found  to  amount  to  .0318  g. 
One  cubic  centimeter  of  the  solution  dissolved,  therefore, 
.003  g.  of  the  lead  salt,  equivalent  to  .00086  g.  of  rubidium. 
The  experiment  was  made  at  about  20°. 

Ccesium-  Plumbic  Chloride,  Cs  PbCl*.  —  This  salt  is  very 
readily  prepared  by  passing  chlorine  into  solutions  containing 
lead  chloride  and  a  large  excess  of  caesium  chloride.  When 
hydrochloric  acid  is  present,  the  excess  of  csesium  chloride  is 
unnecessary,  but  in  that  case  the  precipitate  is  very  finely 
divided.  The  precipitate  begins  to  form  in  solutions  that  are 
nearly  at  a  boiling  temperature.  A  crop  obtained  without  the 
use  of  hydrochloric  acid  was  analyzed.  It  was  washed  with 
hydrochloric  acid  containing  chlorine  and  air-dried. 


OF  LEAD   TETRACHLORIDE. 


319 


Found. 

Caesium 38.51 

Lead 30.05 

Chlorine 30.99 

99.55 

Loss  on  heating      .    .     .    10.96 


ci, 


Calculated  for 
Cs2PbCl6. 

38.78 
30.17 
31.05 
100.00 
10.35 


The  salt  usually  has  a  lemon-yellow  color,  but,  when  very 
strong  hydrochloric  acid  is  used  and  a  large  excess  of  lead 
chloride  is  present,  the  precipitate  has  a  dark  brown  color. 
Such  a  crop  gave  the  following  analysis : 


Found. 

Caesium 38.19 

Lead 29.64 

Chlorine 31.35 

99.18 
11.09 


Calculated  for 
Cs2PbCl«. 

38.78 
30.17 
31.05 
100.00 
C12      10.35 


Loss  on  heating  .    .     . 

This  is  evidently  the  same  compound 
as  the  lemon-yellow  salt.  The  cause  of 
the  brown  color  is  not  known.  The 
presence  of  lead  dioxide  in  it  does  not 
seem  probable  on  account  of  the  strong 
acid  that  was  used,  and,  moreover,  ex- 
periment showed  that  this  oxide  was 
instantly  dissolved  by  the  mother-liquor. 
It  was  suspected  that  this  was  a  dimorphous  form  of  the 
compound,  but  Mr.  Louis  V.  Pirsson,  who  has  kindly  made 
a  microscopic  examination  of  both  products,  has  found  that 
both  are  isometric  and  octahedral  in  habit.  He  noticed  that 
while  the  yellow  salt  forms  perfect  octahedrons,  the  brown 
compound  occurs  in  octahedral  groups  composed  of  combina- 
tions of  the  cube  and  octahedron.  The  accompanying  figure, 
by  Mr.  Pirsson,  shows  the  prevailing  habit  of  these  crystals. 
The  groups  are  very  small,  usually  not  over  0.015  mm. 
in  diameter. 


SHEFFIELD  SCIENTIFIC  SCHOOL, 
March,  1893. 


ON  THE  DOUBLE  HALIDES  OF  ANTIMONY 
WITH  RUBIDIUM.* 

BY  H.  L.  WHEELER. 

THE  investigations  of  the  double  halides  of  antimony  and 
rubidium  have  hitherto  been  confined  to  the  chlorides,  and  the 
following  salts  have  been  described : 

1  :  1    Eubidium  Antimony  Chloride,       EbCl.SbCl8. 

5:3  «  «  «  5RbC1.3SbCl8 

23 :  10         "  "  "  23RbC1.10SbCl8 

6:1          "  "  "  6RbCl.SbCl8 

The  first  three  of  these  compounds  were  described  by  Remsen 
and  Saunders.f  These  investigators,  after  a  careful  study  of 
the  subject,  came  to  the  conclusion  that  the  salt  6RbCl.SbCl8 
described  by  GodeffroyJ  does  not  exist. 

It  has  been  shown  by  the  author  of  the  present  article  that 
the  3  :  2  type  of  double  salts  is  probably  the  only  one  formed 
by  the  combination  of  the  arsenic  halides  with  those  of  csesium 
and  rubidium.  §  Moreover,  since  this  type  was  observed  by 
Sch8effer||  in  the  case  of  the  double  halides  of  antimony  with 
sodium,  potassium,  and  ammonium,  and,  since  Remsen  and 
Saunders  obtained  the  salt  3CsC1.2SbCl3  it  seemed  probable 
that  this  type  of  double  halides  would  exist  with  rubidium 
and  antimony.  A  thorough  re-examination  of  the  chlorides 
has  therefore  been  undertaken,  and  the  investigation  has  been 
extended  to  the  bromides  and  iodides.  As  a  result  of  this 
investigation  the  following  compounds  have  been  obtained : 

KbC1.2SbCl8.H20  

KbCl.SbCl8.  

3RbC1.2SbCl8.  3KbBr.2SbBr8  3RbI.2SbI8 

23RbC1.10SbCl8  (?)  23RbBr.lOSbBr8  (?)  

*  Amer.  Jour.  Sci.,  xlvi,  Oct.,  1893.         t  Amer.  Chem.  Jour.,  xiv,  155. 
$  Berichte,  viii,  9.  §  Amer.  Jour.  Sci.,  xlvi,  88. 

II  Pogg.  Ann.,  cix,  611. 


DOUBLE  HALIDES  OF  ANTIMONY.  321 

The  first  chloride,  RbC1.2SbCl8.H2O,  is  a  new  type  of 
antimony  rubidium  halides,  which  Remsen  and  Saunders  did 
not  obtain.  The  second,  1:1,  confirms  the  results  of  these 
investigators,  while  the  series  of  3  :  2  salts,  which  includes  a 
chloride,  bromide,  and  iodide,  corresponds  to  the  type  expected 
from  analogy.  The  difference  between  the  percentage  compo- 
sition required  for  the  3  :  2  chloride  and  that  required  for  the 
5  :  3  formula  of  Remsen  and  Saunders  is  small,  and  it  is  to  be 
noticed  that  these  authors  do  not  consider  their  formula  as 
definitely  established.  They  say,  "  The  analytical  results  ob- 
tained from  different  samples  varied  considerably  and  it  does 
not  appear  possible  to  obtain  the  salt  in  pure  condition."  It 
will  be  noticed  that  most  of  the  analyses  of  the  3  :  2  chloride, 
made  in  the  present  investigation,  show  a  composition  inter- 
mediate between  what  is  required  for  the  formulas  of  the  3  :  2 
and  the  5  :  3  salts,  but  the  bromide  and  the  iodide  were  readily 
obtained  in  pure  condition  and  gave  analytical  results  closely 
corresponding  to  the  3:2  formula.  Moreover  the  chloride, 
bromide,  and  iodide  just  mentioned  are  all  hexagonal  and  may 
be  referred  to  axes  which  correspond  closely  to  those  of  the 
3  :  2  arsenic  compounds.  The  chloride  and  bromide  with  a 
complex  composition  (23  :  10  ?)  confirm  the  results  of  Remsen 
and  Saunders  on  the  chloride.  The  formula  suggested  by 
them  has  been  retained,  subject  to  uncertainty.  It  will  be 
seen  beyond  that,  as  Remsen  and  Saunders  have  noticed, 
the  ratio  16  :  7  corresponds  very  closely  to  the  analyses,  and 
it  may  be  added  that  the  ratios  9  :  4  and  7  :  3  differ  so  little 
from  the  other  two  that  it  would  be  very  difficult  to  dis- 
tinguish between  any  of  these  ratios  by  analysis. 

For  the  preparation  of  the  double  halides  the  constituents 
were  mixed  in  the  presence  of  the  corresponding  dilute  acids. 
In  the  case  of  the  chlorides  a  10  per  cent  acid  was  used. 
The  mixtures  were  then  evaporated  until  crystals  separated 
on  cooling.  Further  details  will  be  given  with  the  descrip- 
tions of  the  salts.  In  the  case  of  each  salt  several  crops 
were  prepared  and  analyzed,  and  an  attempt  has  been  made 
to  determine  approximately  the  limits  of  the  conditions  under 

21 


322  ON  THE  DOUBLE  HALIDES   OF 

which  these  double  halides  are  formed.  It  may  be  added  that 
the  analytical  results  are  not  selected,  for  with  the  exception 
of  two  antimony  determinations,  where  an  error  had  been 
detected,  every  determination  that  was  made  has  been  given. 

Method  of  Analysis. 

The  salts  were  removed  from  the  mother-liquor,  and,  after 
pressing  on  smooth  filter  paper,  were  dried  in  the  air  for  a 
short  time.  Portions  of  a  little  less  than  half  a  gram  were 
taken  for  analysis.  In  order  to  determine  the  halogens,  silver 
nitrate  was  added  to  a  solution  of  the  substance  in  water 
containing  a  little  tartaric  and  nitric  acids,  the  mixture  was 
then  warmed  on  the  water  bath  for  a  couple  of  hours,  and 
finally,  after  standing  twelve  hours,  the  silver  halide  was  col- 
lected, ignited,  and  weighed  in  a  Gooch  crucible  in  the  usual 
manner.  The  determination  of  the  antimony  and  rubidium 
was  effected  in  a  separate  sample.  In  order  to  do  this,  the 
salts  were  dissolved  in  a  little  dilute  hydrochloric  acid  and  the 
solutions  were  diluted  with  boiling  water.  Hydrogen  sulphide 
was  then  used  to  precipitate  the  antimony,  and,  when  the  solu- 
tions had  cooled,  the  resulting  sulphide  was  filtered  on  asbes- 
tos in  a  Gooch  crucible,  washed  with  water  and  alcohol  and 
then  heated  to  230°  in  an  oven  filled  with  carbonic  acid.  On 
cooling,  the  sulphide  was  weighed  as  Sb2S8.  The  rubidium 
was  determined  by  evaporating  the  filtrate  from  the  antimony 
sulphide  to  dryness  with  an  excess  of  sulphuric  acid,  the 
residue  was  then  converted  into  normal  sulphate  by  ignition 
in  a  stream  of  air  containing  ammonia.  The  atomic  weights 
used  in  the  calculation  of  results  were  the  following  : 

Cl,  35.5 ;  Br,  80  ;  I,  127  ;  Sb,  120  ;  Rb,  85.5 

The  Double  Chlorides. 

The  crystals  of  the  double  chlorides  are  colorless,  with  the 
exception  of  the  salt  3RbC1.2SbCl8 ;  this  salt  has  a  pale  yellow 
color  exactly  similar  to  the  salts  3RbC1.2AsCl8  and  3CsCl. 
2AsCl8.  The  stability  of  the  double  chlorides,  on  exposure, 


ANTIMONY  WITH  RUBIDIUM.  323 

appears  to  vary  inversely  with  the  quantity  of  antimony  chlo- 
ride which  they  contain. 

1:2  Rubidium  Antimony  Chloride,  RbCl.2SbClt.]ItO.- 
This  new  salt  was  obtained  from  hydrochloric  acid  solution 
when  the  constituents  were  mixed  in  the  proportion  of  ten, 
eight,  or  six  molecules  of  SbCl3  to  one  of  RbCl.  On  concen- 
trating these  mixtures  supersaturated  solutions  were  obtained 
which  sometimes  remained  for  days  without  giving  crystals, 
but  on  shaking,  or  stirring  with  a  glass  rod,  the  crystallization 
was  induced.  The  crystals  separate  in  the  form  of  elongated, 
colorless,  monoclinic  tables.  Analysis  of  different  crops  gave : 


From  Solutions  of 
10SbCls  to  IRbCl. 

From  Solution 
of  8SbCl3  to 
IRbCl. 

From 
Solution 
of  6SbCl3 
to  IBbCl. 

Calculated  for 
RbC1.2SbCls.H,O. 

Kb 

14.61 

14.71 

14.74 

14.64 

15.07 

14.44 

Sb 

40.75 

40.97 

41.09 

41.07 

40.97 

40.54 

Cl 

41.83 

41.53 

41.11 

.  .  . 

.  .  . 

41.98 

H20 

3.20 

3.10 

3.18 

3.08 

•  •  • 

3.04 

The  crystals  of  this  salt  have  a  brilliant  lustre  when  first  re- 
moved from  the  mother-liquor,  but  on  exposure  they  soon 
lose  their  lustre,  becoming  opaque  and  decomposing.  In  the 
preparation  of  this  salt  for  analysis  the  crystals  were  crushed 
and  thoroughly  pressed  on  filter  paper,  and  when  it  was  certain 
that  the  powder  did  not  contain  any  mechanically  mixed  water, 
it  was  placed  in  a  weighing-tube.  This  salt  is  readily  dis- 
tinguished from  the  other  colorless  double  halides  of  rubidium 
and  antimony  by  the  fact  that  it  melts  at  77°. 

1  :  1  Rubidium  Antimony  Chloride,  RbC2.SbCls.  —  This  salt 
was  first  described  by  Remsen  and  Saunders  ;  *  they  say  that 
"  if  the  excess  of  antimony  chloride  ...  be  very  great,  a 
colorless  salt  crystallizing  in  elongated,  apparently  orthorhom- 
bic,  crystals  is  obtained."  I  have  found  that  by  mixing  the 
constituents  in  hydrochloric  acid  solutions,  in  the  proportion 
of  four  or  three  molecules  of  SbCl8  to  one  of  RbCl,  crystals  of 
similar  appearance  were  obtained.  The  solutions  require  a 

*  Loc.  cit. 


324  ON   THE  DOUBLE  HALIDES   OF 

considerable  degree  of  concentration,  and  the  mother-liquor  is 
more  or  less  syrupy,  hence  the  rubidium  determinations  came 
low  and  the  antimony  high.  Analysis  gave : 

From  Solution  of  From  Solution  of  Calculated  for 

4SbCl3  to  IRbCl.  3SbCl3  to  IRbCl.  KbCl.SbCl3. 

Eb 23.67  23.96  24.61 

Sb 35.38  34.99  34.53 

Cl 40.70  40.73  40.86 

A  solution  of  antimony  and  rubidium  chloride  in  the  pro- 
portion of  2^  molecules  of  the  former  to  one  of  the  latter 
gave  a  mixture  of  this  salt  and  the  yellow  one  described 
below.  As  has  been  observed  by  Remsen  and  Saunders, 
crystals  of  this  salt  rapidly  lose  their  lustre  on  exposure. 
They  give  no  definite  melting-point  below  the  temperature  of 
boiling  sulphuric  acid. 

3\%  Rubidium  Antimony  Chloride,  3Rt>Cl£SbCl9.  —  Tbis 
is  the  salt  to  which  Remsen  and  Saunders  assign  the  formula 
5RbC1.3SbCl8.  They  obtained  this  compound  on  adding  "  a 
considerable  excess  "  of  antimony  chloride  to  a  solution  of  the 
salt  23RbC1.10SbCl3.  They  describe  the  crystals  as  some- 
times resembling  a  rhombohedron  in  general  shape  and  having 
a  pale  yellow  color,  and  they  remark  that  "  this  is  noteworthy, 
because  the  more  complex  salt  (23RbC1.10SbCl8)  and  the 
simpler  one  (RbCl.SbCl3)  are  both  colorless.  It  is  to  be 
remembered,  however,  that  the  salt  Cs3Sb2Cl9(3CsC1.2SbCl8) 
is  also  yellow."  It  may  be  added  that  both  3CsCl.  2AsCl3  and 
3RbC1.2AsCl8  are  pale  yellow.  Remsen  and  Saunders  also 
remark:  "As  the  formula  of  this  rubidium  salt  is  not  very 
simple,  and  as  the  substance  could  not  be  recrystallized,  on 
account  of  the  strong  tendency  towards  the  formation  of  the 
very  complex  salt,  the  formula  suggested  below  can  hardly  be 
considered  as  definitely  established." 

I  have  found  that  when  solutions  of  antimony  chloride  and 
rubidium  chloride  are  mixed  in  the  proportion  of  one  and  one- 
fifth  molecules  of  the  former  to  one  molecule  of  the  latter  a 
pale  yellow  salt  is  obtained  crystallizing  in  rhombohedra. 


ANTIMONY  WITH  RUBIDIUM. 


325 


In  one  case,  on  obtaining  a  crop  of  crystals  from  a  solution 
of  2SbCl8  to  IRbCl  in  strong  HC1,  the  yellow  rhombohedra 
were  seen  to  be  mixed  with  the  colorless  hexagonal  plates, 
presumably  of  the  salt  23RbC1.10SbCl8.  It  was  also  found 
that  a  wide  difference  exists  in  the  solubility  of  these  two 
salts  in  warm  solutions ;  the  yellow  crystals  dissolved  with 
difficulty,  while  on  the  other  hand  the  salt  23  :  10  went  into 
solution  with  only  a  slight  elevation  of  temperature.  If  the 
crystals  of  the  yellow  salt  are  warmed  in  the  mother-liquor 
they  become  opaque  throughout  without  losing  their  pale  yel- 
low color.  It  seems  probable  that  impurities  are  dissolved  out 
by  this  operation  and  that  no  decomposition  takes  place,  for 
the  decomposition  products  and  the  other  double  chlorides  are 
colorless.  An  analysis  of  a  crop  obtained  in  this  manner  cor- 
responded very  closely  to  the  formula  3RbC1.2SbCl8.  Analy- 
sis gave : 


From 
Solutions  of 
2SbCls  to 
IRbCL 

From 
Solutions  of 
l$SbCl3  to 
IRbCl. 

From 
Solutions  of 
2SbCl3  to 
IRbCl 
heated. 

Calculated 
for 
3RbCl. 
2SbCl8. 

Calculated 
for 
5RbCl. 
3SbCl8. 

Kb 

32.57 

32.19 

33.34 

31.86 

31.30 

31.44 

33.28 

Sb 

28.68 

28.67 

28.55 

28.46 

29.44 

29.41 

28.03 

Cl 

38.38 

38.42 

38.32 

... 

38.98 

39.15 

38.69 

23:10?  Rubidium  Antimony  Chloride, 
-  For  the  preparation  of  this  compound,  a  sample  of  rubidium 
chloride  was  used  which  had  been  specially  purified  for  the 
purpose  by  the  method  recently  described  by  Prof.  H.  L. 
Wells*  of  this  laboratory.  The  purification  of  this  sample 
was  repeated  after  the  product  failed  to  give  spectroscopic 
reactions  for  potassium  and  caesium. 

If  solutions  of  antimony  and  rubidium  chlorides  are  mixed 
in  the  proportion  of  one  molecule  of  SbCl  to  one,  four,  or 
six  molecules  of  RbCl,  the  crystals  obtained  are  the  "  color- 
less six-sided  plates,  tables,  or  thicker  crystals,"  to  which 
Remsen  and  Saunders  have  assigned  the  formula  23RbCl. 
10SbCl8.  The  average  results  of  the  analyses  of  the  different 

*  Amer.  Jour.  Sci.,  HI,  xlvi,  188. 


326  ON   THE  DOUBLE  HALIDES   OF 

crops  of  the  double  chloride  gave  figures  closely  agreeing  with 
those  of  the  above  authors,  but  the  ratio  of  rubidium  to  anti- 
mony came  somewhat  lower  than  theirs.  Analysis  gave  : 


From 
Solution 
6RbCl  to 

From 
Solution 
4RbCl  to 

From 
Solution 
IRbCl  to 

Sample 
recrystal- 
lized  from 

Average. 

Ratio. 

18bCl3. 

18bCl3. 

18bCl3. 

10%  HCL 

Eb 

38.98 

38.55 

38.83 

38.62 

38.60 

38.716 

2.28 

Sb 

23.76 

23.98 

23.52 

23.81 

23.767 

1.00 

m 

37.16 

36.97 

36.95 

37.026 

5.26 

culated  for 
)C1.10SbCls. 

38.96 

Calculated  for 
!GRbC1.7SbCl3. 

38.85 

Calculated  for 
9RbC1.4SbCl8. 

38.57 

Calculated  for 
7RbC1.3SbCl3. 

39.21 

23.77 

23.86 

24.06 

23.58 

37.27 

37.29 

37.37 

37.21 

Kb    . 

Sb     . 
Cl      . 

It  is  to  be  noticed  that  this  salt  is  formed  under  conditions 
varying  more  widely  than  in  the  case  of  any  of  the  other  double 
rubidium  antimony  chlorides.  It  can  be  exposed  to  the  air  for 
several  days  without  losing  its  lustre;  on  long  exposure  it 
becomes  covered  with  a  white,  opaque  layer,  probably  of  anti- 
mony oxychloride. 

The  Double  Bromides. 

The  bromides  were  obtained  in  the  form  of  brilliant  yellow, 
six-sided  plates,  resembling  the  double  arsenic  bromides  of 
rubidium  and  caesium.  They  are  comparatively  stable  in  the 
air,  but  on  long  exposure  the  crystals  lose  their  lustre. 

3  :  2  Rubidium  Antimony  Bromide,  3RbBr.2SbBry  —This 
salt  was  obtained  from  dilute  hydrobromic  acid  solutions  when 
the  constituents  were  mixed  in  the  proportion  of  two  and  three- 
tenths  and  also  four  molecules  of  RbBr  to  one  of  SbBr3 ;  it 
was  also  the  only  one  formed  when  antimony  bromide  was 
present  in  the  solutions  in  excess.  It  will  be  seen  that  a  much 
larger  range  of  conditions  exists  for  the  preparation  of  the  salt 
3RbBr.2SbBr8  than  in  the  case  of  the  corresponding  double 
chloride.  Moreover,  the  bromide  can  be  recrystallized  unaltered 
from  dilute  hydrobromic  acid. 


ANTIMONY   WITH  RUBIDIUM. 


327 


Analysis  gave : 


From  Solutions 
containing  a 
large  Excess  of 
SbBr3. 

From 
Solution 
23RbBr. 
to  10SbBr3. 

From 
Solution 
4RbBr  to 
!SbBrs. 

Sample 
of  Latter 
recrystal- 
lized  from 
HBr. 

Calculated, 
for 
SRbBr. 

2SbBr3. 

21.55 

21.18 

20.96 

21.16 

21.53 

20.92 

21.08 

.  •  • 

20.07 

20.13 

19.98 

19.59 

19.91 

19.73 

59.30 

59.07 

59.19 

Rb 
Sb 
Br 


23  :  10  (?)  Rubidium  Antimony  Bromide,  23  RbBr.  10  SbBr&. 
—  This  salt  was  obtained  when  dilute  hydrobromic  acid  solu- 
tions of  rubidium  and  antimony  bromides  were  mixed  in  the 
proportion  of  six,  eight,  and  •  thirteen  molecules  of  the  former 
to  one  of  the  latter.  The  crystals  obtained  on  slowly  cooling 
these  mixtures,  with  the  exception  of  their  strong  yellow  color, 
closely  resemble  the  corresponding  complex  chloride.  If  the 
solutions  are  rapidly  cooled  the  salt  separates  in  the  form  of 
brilliant  spangles.  The  average  of  the  following  results  gives 
a  remarkably  close  ratio  to  that  required  for  the  formula 
23RbBr.lOSbBr8. 

Analysis  gave: 


Rb 
Sb 
Br 


Solution 
GRbBr  to 
ISbBrg. 

26.66 
16.11 

Solution 
SRbBr  to 
18bBrs. 

26.16 

16.23 

From  Solution 
ISRbBr  to  ISbBr,. 

Sample 
of  Latter 
recrystallized 
from 
cone.  HBr. 

26.39 
16.18 
57.41 

26.92 
16.18 
57.27 

26.60 
16.26 
57.23 

26.71 
16.22 

Rb 

Calculated  for 
23RbBr.lOSbBr8. 

.    .    26.55 

Calculated  for 
16RbBr.7SbBr8. 

26.47 

Calculated  for 
9RbBr.4SbBr8. 

26.27 

Calculated  for 
7RbBr.3SbBrs. 

26.74 

Sb 

.    .     16.20 

16.25 

16.38 

16.08 

Br 

57.25 

57.28 

57.35 

57.18 

Average  of 

analytical  Ratios  derived 

Results. 

Rb  .  .  26.57  .3107  or  23.03  or  16.12  or  9.21  or  6.90 
Sb  .  .  16.19  .1349  "  10.00  "  7.00  "  4.00  "  3.00 
Br  .  .  57.30  .7162  «  53.09  «  37.16  "  21.23  "  15.92 

It  is  to  be  noticed  that  this  salt  is  formed  within  a  much 
smaller  range  of  conditions  than  in  the  case  of  the  chloride,  and 


328  ON  THE  DOUBLE  HALIDES   OF 

can  only  be  recrystallized  from  strong  hydrobromic  acid  solu- 
tions. When  recrystallized  from  moderately  strong  acid  a 
mixture  of  the  salts  23  :  10  and  3  :  2  was  obtained,  but  from 
dilute  acid  a  pure  crop  of  the  3  :  2  compound  separated. 

Recrystallized  Recrystallized  Calculated  for 

from  strong  from  dilute  SRbBr  l)SbBr 

HBr.  HBr. 

Kb 25.54  21.89  21.08 

Sb 16.93  19.70  19.73 

Br 57.77  .  .  .  59.19 

The  Double  Iodide. 

3:2  Rubidium  Antimony  Iodide,  3R.bI.2SbIz. —  The  for- 
mation of  this  salt  was  observed  when  a  solution  of  rubidium 
iodide  in  hydriodic  acid  was  saturated  hot  with  antimony 
iodide ;  it  was  also  obtained  from  a  solution  of  antimony  iodide 
in  a  large  excess  of  rubidium  iodide.  The  best  crystals  are 
obtained  when  a  considerable  quantity  of  antimony  iodide  is 
present ;  under  these  conditions  large  deep  red  lozenge-shaped 
crystals  separate.  Analysis  gave : 

Large  Excess  Large  Excess  Calculated  for 

of  Rbl.  of  SbI8.  3KbI.'28bI8. 

Kb 16.28  14.82  15.64 

Sb 14.14  15.17  14.64 

I 69.76  69.55  69.72 

On  exposure  to  the  air  the  crystals  slowly  lose  their  lustre. 

Crystallography. 

The  crystallization  of  the  3  :  2  double  salts  is  hexagonal. 
In  general  the  habit  is  rhombohedral  and  they  can  all  be  re- 
ferred to  axes  of  nearly  equal  length.  The  double  bromide 
and  iodide  have  a  perfect  basal  cleavage,  like  the  salts  of  the 
arsenic  series,  while  the  chloride  gave  only  a  conchoidal  frac- 
ture. The  axial  ratios  of  the  salts  is  shown  by  the  following 
table,  the  ratios  of  the  corresponding  arsenic  salts  being  given 
for  comparison. 


ANTIMONY  WITH  RUBIDIUM. 


329 


a    :    c  a    :    c  arc 

3RbC1.2SbCl3      1  :  1.125  3RbC1.2AsCl3  1  :  1.210  3CsC1.2AsCl8  1  :  1.209 

3RbBr.2SbBr8    1  :  1.207  3RbBr.2AsBr3  1  :  1.220  3CsBr.2AsBr8  1  :  1.219 

3RbI.2SbI8         1  :  1.230  3RbI.2AsI3  1  :  1.242  3CsI.2A8l3  1  :  1.244 

From  this  table  it  may  be  seen  that  the  substitution  of 
arsenic  by  antimony  produces  little  if  any  effect  in  the  lengths 
of  the  axes,  and  in  each  series 
the  vertical  axes  lengthen  as  the 
atomic   weight    of    the    halogen 
increases. 

3Kb  Cl.2SbCl3.  — This  salt,  un- 
like the  others  of  the  series,  shows 
rhombohedral  tetartohedrism.  In 
one  crop,  where  the  crystals  meas- 
ured 5  to  7  mm.  in  diameter,  the 

faces  were  developed  on  every  crystal  as  in  Fig.  1,  the  forms 
being 

a,  1120,  i-2  e,  01T2,  -£  y,  2532, 


Fig.  1. 


m,  10TO,  / 


v,  T322,  — 


On  a  second  crop  only  e  and  a  were  developed. 

Calculated. 


e  A  e,  01T2  A  1T02 
e  A  v,  01T2  A  T322 
e  A  ?/,  T322  A  2532 
y  A  a,  25H2  A  T2TO 


Measured. 

56°  18' 
29°  53' 
11°  29' 

20°  29' 


29°  55' 
11°  26' 
20°  29' 


This  salt  differs  from  all  the  others  of  the  series,  since  it  is 
the  only  one  on  which  tetartohedrism  has  been  observed. 
Whether  the  others  are  really  tetartohedral,  but  have  not 
shown  it  owing  to  the  absence  of  highly  modified  forms,  can- 
not be  told  at  present.  Also  the  basal  cleavage,  which  is  so 
prominent  on  all  of  the  others,  could  not  be  detected,  while 
the  one-half  rhombohedron  e  was  only  observed  on  this  salt. 
A  basal  section  was  prepared,  which  in  convergent  polarized 
light  showed  a  normal,  uniaxial  interference  figure,  the  double 
refraction  being  negative,  like  the  corresponding  arsenic 
compound. 


330 


ON  THE  DOUBLE  HALIDES  OF 


Fig.  2. 


3RlBr.2SbBr*.  —  Crystals 
of  this  salt  were  prepared  up 
to  7mm.  in  diameter.  The 
habit  is  generally  that  of  six- 
sided  plates,  Fig.  2,  having  the 
forms  c,  0001,  0;  r,  1011,  1 
and  2,  0111,  —  1.  In  one  crop 
<?,  r,  and  m  were  developed  with 
Fig.  s.  some  of  the  rhombohedral  faces 

predominating  to  such  an  ex- 
tent that  the  crystals  looked  like  prisms,  represented  in  basal 
projection  by  Fig.  3. 


r/\c,  10T1  A  0001 
r  A  z,  10T1  A  01T1 


Measured. 

*52°  21' 
48°    0' 


Calculated. 


47°  57' 


None  of  the  crystals  show  normal  optical  properties.  Crys- 
tals like  Fig.  3  showed  for  the  most  part  an  extinction  parallel 
to  the  direction  c-d,  sometimes  with  twinned  lamellse  promi- 
nent at  one  end.  In  convergent  polarized  light  no  interference 
figure  was  observed  normal  to  c,  but  some  of  the  crystals  like 
Fig.  3  could  be  tilted  up  on  a  rhombohedron  face  and  showed 
an  acute  bisectrix  nearly  normal  to  r.  The  axial  angle  was 
small  and  the  dispersion  strong,  the  optical  axes  being  in  the 
plane  a— b  for  green  and  normal  to  that  for  red  light,  the  inter- 
ference figure  looking  like  that  of  brookite. 

3RbI.2Sbls.  —  This  salt,  unlike  the  corresponding  arsenic 
compound,  was  obtained  in  crystals  of  considerable  size,  some 
over  10  mm.  in  diameter.  When  prepared  with  an  excess  of 
SbI8,  usually  lozenge-shaped  crystals  were  obtained,  shown  in 
basal  projection  in  Fig.  4.  These  were  often  grouped  in  twin 
position,  penetration  twins  being  prominent  with  a  rhombo- 
hedron as  twinning  plane.  From  solutions  containing  an 
excess  of  Rbl,  the  rhombohedral  habit  was  observed,  some- 
times with  a  negative  scalenohedron  s  18.9.17, -^y-f,  bevel- 
ling its  pole  edges,  Fig.  5. 


ANTIMONY   WITH  RUBIDIUM. 


331 


m  A  r,  10TO 
r  A  c,  10T1 
r  A  3,  10T1 
r  A  r,  10T1 

S  A  5,  18517 


A  10T1 
A  0001 

A  0111 
A  1101 

A  19817 


Measured. 

*35°    6' 

54°  43' 

47°  15' 

89°  50' 

6°  40' 


Calculated. 
48°  18' 

48°  18' 

90°  14' 

6°  21' 


The  basal  cleavage  was  prominent,  and  sections  parallel  to 
this  showed  abnormal  optical  properties.  Thin  plates  from 
the  crystals  like  Fig.  4  showed  middle  and  end  sections  with 


Fig.  4. 


Fig.  5. 


extinctions  in  the  directions  indicated  by  the  arrows.  In 
convergent  light  no  interference  figure  was  observed.  This 
salt  then,  like  3RbBr.2SbBr8  and  3RbI.2AsI3,  is  only  pseudo- 
hexagonal,  being  abnormal  in  its  optical  properties. 

Rb  CLSb  C13.  —  The  crystalli-        

zation  of  this  salt  is  monoclinic. 
Crystals  were  obtained  10  mm. 
long.  The  forms  observed 
were 


Fig.  6. 


a,  100,  i-l 
c,  001,  0 


m,  110,  / 
d,  101,  - 


e,  T01,  1-f 
#111,  1 


The  habit  is  shown  in  Fig.  6.     The  axial  ratio  is  d :  b :  c= 
1.732 : 1.000 : 1.085 ;  ft  =  001  A  100  =  65°  34'. 


332 


ON  THE  DOUBLE  HALIDES  OF 


a  A    c,  100  A  001 

a  A  m,  100  A  110 

c  A   e,  001  A  T01 

WA  w,  110  AT10 

a'  A   e,  TOO  A  T01 

p  A   e,  TT1  A  T01 

p  A   c,  TT1  A  001 

c  A  d,  001  A  101 

d  A  a,  101  A  100 


Measured. 

Calculated. 

*65°  34' 

.   .   . 

*57°  37' 

.    .   . 

*37°  36' 

... 

64°  46' 

64°  46' 

76°  54' 

76°  50' 

46°  28' 

46°  23' 

56°  50' 

56°  52' 

24°  21' 

24°  22' 

41°  24' 

41°  12' 

772 


Fig.  7. 


In  polarized  light  these  crystals  show  an 
extinction  parallel  to  the  ortho-axis.  With 
crystals  flattened  parallel  to  the  basal  plane 
an  obtuse  bisectrix  may  be  seen  nearly 
normal  to  the  base,  the  plane  of  the  optical 
axis  being  at  right  angles  to  the  symmetry 
plane. 

EbCU&S'bCli.H.fl.  —  The  crystallization  of 
this  salt  is  monoclinic.  Crystals  were  made 
up  to  a  length  of  about  9  or  10  mm.  The 
forms  observed  were : 


a,  100,  i-i 

c,  001,  0 

m,  110,  I 


d,  021,  2-^ 

e,  Oil,  14 


p,  221,  -2 
a,  T01,  1-* 


The  habit  is  shown  in  Fig.  7.     The  axial  ratio  is  d :  b :  c  1.699  : 
1 :  0.820 ;  /?  =  001  A  100  =  89°  28  J'. 


m*m,  110  A  T10 
a  A  a,  100  A  T01 
m  A  a,  110  A  100 
a  A  c,  100  A  001 
x  A  c,  T01  A  001 
c  A  e,  001  A  Oil 
c  A  d,  001  A  021 
a  A  p,  100  A  221 
p  A  d,  221  A  021 


Measured. 

Calculated. 

*60°  57' 

.    •    . 

64°  49' 

64°  40' 

59°  32' 

59°  32' 

*89°  28^' 

.  •  • 

*25°  51£' 

.  .  . 

39°  10' 

39°  21' 

58°  20' 

58°  37' 

63°    5' 

63°    6' 

27°    5' 

26°  37' 

ANTIMONY   WITH  RUBIDIUM.  333 

The  crystals  flattened  parallel  to  the  orthopinacoid  show  in 
polarized  light  an  extinction  parallel  to  the  ortho-axis,  and  in 
convergent  light  a  bisectrix  and  one  of  the  ring  systems  appear 
near  the  limits  of  the  field.  The  plane  of  the  optical  axis  is 
the  clinopinacoid. 

The  23 : 10  bromide  is  pseudohexagonal.  Basal  plates 
always  showed  an  intricate  twinning  when  examined  in  polar- 
ized light.  The  pyramidal  faces  were  horizontally  striated 
and  to  such  an  extent  that  no  satisfactory  measurements  could 
be  made.  In  every  respect  this  compound  resembles  the 
23 :  10  chloride  described  by  Remsen  and  Saunders. 

In  conclusion  the  author  wishes  to  express  his  indebtedness 
to  Prof.  H.  L.  Wells  for  valuable  advice  in  connection  with 
the  present  investigation  and  to  Prof.  S.  L.  Penfield,  under 
whose  generous  supervision  the  crystallography  of  these  salts 
was  investigated. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
June,  1893. 


ON  THE    DOUBLE    CHLORIDES,   BROMIDES,  AND 
IODIDES   OF   CAESIUM   AND   CADMIUM.* 

BY  H.  L.   WELLS  AND  P.  T.  WALDEN. 

SINCE  the  caesium-mercuric  halides  f  had  been  studied  by 
one  of  us  with  the  result  that  six  types  of  double  salts  were 
found,  it  seemed  desirable  to  extend  the  investigation  to  the 
metal  cadmium  on  account  of  its  close  relation  to  mercury. 
We  have,  therefore,  undertaken  this  work,  and  as  the  result  of 
a  systematic  and  very  thorough  search  have  obtained  the  fol- 
lowing compounds.  The  salt  Cs2CdCl4  had  already  been 
described  by  Godeffroy. 

3  : 1  Type.  2  : 1  Type.  1  : 1  Type. 

....  Cs2CdCl4  CsCdCl8 

Cs3CdBr5  Cs2CdBr4  CsCdBr3 

Cs8CdI5  Cs2CdI4  CsCdI8.H20 

These  cadmium  salts  correspond  to  the  three  types  of  mercuric 
compounds  which  contain  the  largest  proportion  of  caesium, 
and  no  evidence  of  the  existence  of  cadmium  double  halides 
analogous  to  the  2  :  3, 1 :  2,  and  1 :  5  types  of  caesium-mercuric 
salts  could  be  obtained.  It  is  evident  that  the  tendency  to 
form  a  variety  of  double  halides  decreases  from  mercury  to 
cadmium. 

Three  types  of  cadmium  double  halides  with  alkali  metals 
and  ammonium  have  been  previously  described,  and  a  list  of 
these  is  as  follows : 

4  : 1  Type.  2  : 1  Type.  1  : 1  Type. 

(NH4)4CdCl6  (NH4)2CdCl4.H20  KCdCl34H20 

K4CdCl6  Na2CdCl4.3H20  NaCdBr8.2|H2O 

(NH4)4CdBr6  K2CdCl4  KCdBr84H20 

K4CdBre  K2CdCl4.H20  NH4CdBr84H2O 

(NH4)2CdI4.2H20  NH4CdF8 

Na2CdI4.6H20  

K2CdI4.2H20  

*  Amer.  Jour.  Sci.,  xlvi,  December,  1893.  t  Ibid.,  Ill,  xliv,  221. 


CHLORIDES,  ETC.,   OF  CAESIUM  AND   CADMIUM.       335 


It  is  noticeable  that,  while  the  2  :  1  and  1  :  1  salts  in  the 
above  table  correspond  to  two  types  of  the  caesium  salts  which 
we  have  prepared,  the  4  :  1  type  of  ammonium  and  potassium 
compounds  differs  from  our  3  :  1  caesium-cadmium  salts  and 
from  the  corresponding  caesium-mercuric  compounds.  We 
were  entirely  confident  that  our  results  were  correct,  for  the 
salts  were  well  crystallized  and  carefully  prepared  for  analysis, 
and  it  was  impossible  to  believe  that  we  had  obtained  too  little 
caesium  in  our  analyses,  because  the  salts  of  this  type  were 
crystallized  from  solutions  containing  a  large  excess  of  caesium 
halide.  In  order  to  convince  ourselves  that  there  was  no  mis- 
take about  the  4  :  1  formulas  we  have  prepared  the  two  chlo- 
rides according  to  the  directions  of  Von  Hauer  who  described 
them.  The  salts  were  extremely  well  crystallized  and  it  was 
easy  to  obtain  them  in  a  very  pure  condition.  The  results  of 
the  analyses  were  as  follows : 


Potassium  . 
Cadmium  . 
Chlorine 


Ammonium  .  . 
Cadmium  .  .  . 
Chlorine  .  .  . 

These  results  confirm  Von  Hauer's  formulae,  and  the  curious 
fact  must  be  accepted  that  caesium  forms  3  :  1  double  halides 
with  cadmium,  while  potassium  and  ammonium  form  salts  of 
the  4  :  1  type. 

The  four  types  of  cadmium  double  halides  now  known  form 
a  very  simple  and  symmetrical  series,  the  ratios  of  the  alkali 
metal  to  cadmium  being  4  :  1,  3  :  1,  2  :  1,  and  1  :  1.  The  first 
two  of  these  types  do  not  conform  to  Remsen's  so-called  law  * 
concerning  the  composition  of  double  halides. 

Preparation  and  General  Properties.  —  The  compounds  to 
be  described  were  prepared  by  making  warm  solutions  of  the 

*  Am.  Chem.  Jour.,  xi,  291. 


Found. 

Calculated  for 
K4CdCl«. 

32.35 

32.49 

23.39        23.36 

23.27 

44.00        44.12 

44.24 

Found. 

Calculated  for 
(NH4)4CdClfl. 

18.20 

18.12 

27.91         27.87 

28.22 

53.50 

53.66 

336     DOUBLE   CHLORIDES,  BROMIDES,  AND  IODIDES 

component  halides,  and  after  concentrating  if  necessary,  cool- 
ing to  crystallization.  Water,  slightly  acidified  with  the  cor- 
responding acid  to  prevent  the  formation  of  basic  compounds, 
was  used  as  the  solvent,  and  in  one  instance,  where  a  solution 
became  syrupy  from  a  large  excess  of  a  cadmium  salt,  alcohol 
was  also  tried,  but  without  any  advantage.  The  conditions 
were  varied  gradually  in  each  case  all  the  way  from  the  point 
where  the  solution  was  saturated  with  the  caesium  halide  to 
the  point  where  it  was  saturated  with  the  cadmium  halide, 
and  so  many  experiments  were  made  that  we  believe  that  no 
double  salt,  capable  of  existence  at  the  temperatures  used, 
was  overlooked.  It  was  noticed  that  variations  in  the  concen- 
tration of  any  given  solution  had  little  effect  upon  the  identity 
of  the  salt  produced.  In  this  respect  the  cadmium  compounds 
differ  considerably  from  those  of  mercury,  for  with  the  latter 
concentration  is  often  an  important  factor  in  determining  the 
salt  produced. 

The  three  1  :  1  compounds  CsCdCls,  CsCdBr3,  and  CsCdl,. 
H2O  and  also  the  2:1  iodide  Cs2CdI4  are  capable  of  being 
recrystallized  from  water  unchanged.  The  salt  Cs2CdCl4, 
when  dissolved  in  water,  yields  CsCdCl3,  the  two  bromides 
Cs3CdBr6  and  Cs2CdBr4  yield  CsCdBr3,  while  the  iodide  Cs8CdI5 
gives  Cs2CdI4.  These  facts  show  that  the  salts  having  the 
larger  proportions  of  caesium  require  the  presence  of  an  excess 
of  caesium  halide  for  their  formation.  The  1  :  1  salts  all  crys- 
tallize unchanged  from  extremely  concentrated  solutions  of 
the  corresponding  cadmium  halides. 

All  the  salts  are  colorless.  A  pale  violet  color  noticed  in  a 
few  crops  of  the  bromide  Cs2CdBr4  is  supposed  to  have  been 
due  to  some  unknown  foreign  substance. 

The  solubility  of  the  analogous  salts  in  water  or  in  saline 
solutions  evidently  increases  from  the  chlorides  to  the  iodides. 
The  iodides  consequently  yield  the  largest  crystals,  while  the 
chlorides  give  the  smallest. 

Methods  of  Analysis.  —  The  products  were  carefully  exam- 
ined, and  nothing  was  analyzed  that  was  not  homogeneous. 
The  crystals,  which,  in  several  instances,  were  large  and  fine 


OF  CESIUM  AND   CADMIUM.  337 

and  in  no  case  hygroscopic,  were  freed  from  mother-liquor 
with  great  care  by  pressing  and  crushing  them  on  smooth 
filter-paper.  They  were  then  simply  air-dried  for  analysis. 

Cadmium  was  precipitated  as  sulphide,  this  was  dissolved 
in  hydrochloric  acid  containing  bromine,  and  after  the  free  acid 
had  been  removed  by  evaporation,  the  cadmium  was  precipi- 
tated with  potassium  carbonate  solution,  and  cadmium  oxide 
was  weighed  on  a  Gooch  filter.  The  caesium  in  the  filtrate 
from  the  cadmium  sulphide  was  determined  as  normal  sulphate. 
The  halogens  were  determined  in  separate  portions  by  the 
usual  gravimetric  method. 

In  every  case  at  least  two  separate  crops  of  a  salt  were 
made  and  analyzed,  so  as  to  avoid  any  chance  of  mistakes 
arising  from  mixtures. 

2:1  C cesium- Cadmium  Chloride,  Cs2CdCl^. —  This  salt  is 
produced  as  a  precipitate  when  a  solution  of  cadmium  chloride 
is  added  to  a  concentrated  caesium  chloride  solution.  The 
precipitate  dissolves  upon  warming  the  liquid,  and  crystallizes 
out  in  very  small,  rectangular  plates  when  the  solution  is 
cooled.  Its  formation  was  observed  when  50  g.  of  caesium 
chloride  and  3  g.  of  cadmium  chloride  were  used,  and  it  con- 
tinued to  be  produced  with  the  same  amount  of  caesium  chloride 
until  the  amount  of  cadmium  chloride  had  been  increased  to 
18  g.,  at  which  point  the  1  :  1  salt  began  to  form.  The  salt 
is  very  sparingly  soluble  in  caesium  chloride  solutions,  and  it 
is  probably  due  to  this  fact  that  no  chloride  of  the  3  :  1  type 
could  be  obtained. 

Three  separate  crops  gave  the  following  results  on  analysis : 

Found.  Calculated  for 


Caesium  .    .     .    51.55  51.26  51.51  51.35 

Cadmium     .     .    21.45  21.50  .  .  .  21.62 

Chlorine       .     .    27.03  27.14  26.90  27.03 

100.03  99.90  100.00 

1:1  Ccesium- Cadmium  Chloride,  CsCdCly — This  was  ob- 
tained only  as  a  white  crystalline  powder.     It  is  formed  under 

22 


338     DOUBLE   CHLORIDES,  BROMIDES,  AND  IODIDES 

a  very  wide  range  of  conditions,  being  produced  by  the  re- 
crystallization  of  the  preceding  salt,  and  continuing  to  appear 
until  the  solution  is  saturated  with  cadmium  chloride.  It  is 
very  difficultly  soluble,  especially  in  concentrated  cadmium 
chloride  solutions,  and  it  can  be  recrystallized  unaltered  from 
water.  Two  samples,  obtained  under  widely  different  condi- 
tions, were  analyzed. 


Caesium  ....     38.11  37.60  37.84 

Cadmium     .     .     .     31.80  31.97  31.86 

Chlorine      .     .     .    30.17  30.25  30.30 

100.08  99.82  100.00 

3:1  Ccesium-  Cadmium  Bromide,  Os3  CdBr^.  —  This  com- 
pound was  obtained  in  the  form  of  rectangular  plates,  some- 
times as  much  as  10  mm.  in  diameter.  It  can  be  made  from  a 
solution  of  80  g.  of  caesium  bromide  and  4.5  g.  of  cadmium 
bromide  in  sufficient  water  to  make  a  volume  of  120  c.  c.  On 
recrystallization  it  gives  CsCdBr3. 

Two  separate  samples  were  analyzed. 


Found. 

Cs3CdBr5 


Caesium        .     .     .     44.25  44.27  43.80 

Cadmium     ...     11.88  .  .  .  12.29 

Bromine       .     .     .     43.79  43.77  43.91 

99.92  100.00 


2:1  Caesium- Cadmium  Bromide,  Cs^CdBr^. —  This  was 
obtained  in  the  form  of  slender  needles,  usually  colorless,  but 
sometimes  possessing  a  pale  violet  color  for  some  unknown 
reason.  A  solution  120c.  c.  in  volume,  containing  3g.  of 
cadmium  bromide  and  52  g.  of  caesium  bromide  gave  this  salt. 
When  recrystallized  from  water,  it  gives,  like  the  preceding 
salt,  the  compound  CsCdBrs. 

The  following  analyses  of  separate  crops  were  made.  No. 
IV  was  a  simple  of  the  pale  violet  variety. 


OF  CESIUM  AND   CADMIUM.  339 


_  _  ^  Calculated  for 

T  II.  III.  IV.  ^  Cs2CdBr4. 

Cs   .     .     .     40.46  40.53  .  .  .  40.46  38.11 

Cd  .     .     .     14.55  14.62  14.68  14.78  16.05 

Br   .     .     .     45.12  44.97  45.04  45.04  45.84 

100.13  100.12  100.28  100.00 

Although  the  analyses  agree  well  among  themselves,  it  is 
noticeable  that  they  vary  considerably  from  the  calculated 
composition.  This  disagreement  is  probably  due  to  contamina- 
tion with  caesium  chloride,  resulting  from  the  large  surface 
exposed  by  the  slender  crystals  and  the  concentration  of  the 
mother-liquor.  Moreover,  analogy  with  the  chloride  and  iodide 
makes  the  simple  formula  Cs2CdBr4  far  more  probable  than  the 
complicated  formula  Cs7Cd8Br18  with  which  the  analyses 
correspond. 

1:1  Ccesium-  Cadmium  Bromide,  Cs  CdBrs.  —  The  condi- 
tions under  which  this  compound  is  formed  are  very  wide  in 
range,  for  it  is  produced  by  recrystallizing  Cs8CdBr6,  and  it 
continues  to  appear  as  cadmium  bromide  is  added  until  the 
solution  is  saturated  with  this  very  soluble  salt. 

The  compound  is  evidently  dimorphous.  One  form  occurs 
as  a  crystalline  precipitate,  apparently  isometric  in  form,  under 
narrow  limits  of  conditions  when  caesium  bromide  is  in  excess, 
being  produced  when  Cs3CdBr6  is  recrystallized  from  water. 
The  other  form  occurs  in  well-crystallized  prisms,  and  is 
obtained  when  Cs2CdBr4  is  recrystallized  and  when  cadmium 
bromide  is  in  excess  of  this  proportion.  It  is  interesting  to 
notice  that  we  have  described  a  caesium-lead  bromide  *  of  this 
type,  CsPbBr8,  which  is  dimorphous,  and  that  one  of  us  has 
described  the  dimorphous  mercuric  compounds,!  CsHgCl3  and 
CsHgBr3,  which  also  belong  to  the  same  type. 

Below  are  the  analyses  of  four  separate  samples.  Number 
IV  is  the  granular,  isometric  salt  ;  the  others  represent  the 
prismatic  compound. 

*  Amer.  Jour.  Sci.,  xlv,  128. 
t  Ibid.,  xliv,  225  and  228. 


340     DOUBLE   CHLORIDES,  BROMIDES,  AND  IODIDES 


Calculated  for 


34.85 

34.89 

34.78 

vqgVNUfi 

34.82 

9.78 

9.79 

9.84 

9.55 

9.77 

55.23 

55.35 

55.32 

55.36 

55.41 

t  _  _  ^ 

T  U.  III.  IV?  CsCdBr3. 

Cs   .    .     .    27.67  27.48  .  .  .  27.95  27.42 

Cd  .     .    .    22.97  23.08  22.87  22.92  23.09 

Br  .    .     .    49.49  49.42  49.33  49.30  49.49 

100.13  99.98  100.17  100.00 

3  :  1  Ccesium-  Cadmium  Iodide,  Css  CdI5.  —  This  salt  crystal- 
lizes beautifully  in  large,  stout,  twinned  prisms  which  show  a 
variety  of  habits.  Some  of  the  crystals  obtained  were  as 
much  as  50mm.  in  diameter.  Its  formation  was  observed 
when  182  g.  of  caesium  iodide  and  65  g.  of  cadmium  iodide  were 
dissolved  in  sufficient  water  to  make  a  volume  of  200  c.  c. 

Four  crops  gave  the  following  results  on  analysis  : 

Found.  Calculated  for 

Cs  .    .    . 

Cd  .    .    . 
I     ... 

99.86     100.03      99.94  100.00 

2:1  Ccesium-  Cadmium  Iodide,  C82CdI±.  —  This,  like  the 
corresponding  mercuric  salt,  crystallizes  in  nearly  square  plates, 
in  prisms,  and  in  intermediate  forms.  Some  of  the  plates 
obtained  were  50  or  75  mm.  in  diameter.  It  can  be  prepared 
by  recrystallizing  Cs8CdI5  from  water,  and  as  the  proportion 
of  cadmium  iodide  is  increased,  it  continues  to  form  until  the 
ratio  of  cadmium  to  caesium  has  almost  reached  1:1.  The 
range  of  its  formation  is,  therefore,  much  greater  than  that  of 
the  corresponding  chloride  and  bromide,  and  it  also  differs 
from  these  in  being  recrystallizable  from  water.  Three  different 
samples  were  analyzed. 

Caesium  . 
Cadmium 
Iodine 

100.09      100.11  100.00 

1:1  Ccesium-Cadmium  Iodide,  CsCdTs.ffzO.  —  This  salt 
forms  thin  plates,  often  20  to  30  mm.  in  diameter.  It  is  the 


Found. 

Calculated  for 

Cs3CdI4. 

30.03 

29.85 

30.29 

30.23 

12.56 

12.53 

12.46 

12.64 

.  .  . 

57.27 

57.42 

57.33 

OF  CAESIUM  AND   CADMIUM.  341 

only  hydrous  caesium-cadmium  halide  that  we  have  obtained, 
and  it  is  stable  when  exposed  to  the  air  at  ordinary  temperatures. 

It  was  considered  doubtful  whether  the  corresponding 
caesium  mercuric  iodide  *  contained  a  molecule  of  feebly  com- 
bined water  or  not,  but  since  both  the  cadmium  and  mercuric 
salts  crystallize  in  thin  plates,  it  is  now  believed,  from  analogy, 
that  the  mercuric  compound  was  really  hydrous. 

The  compound  under  consideration  is  formed  under  wide 
limits  of  conditions  when  the  cadmium  present  is  atomically 
equivalent  to  or  in  excess  of  the  caesium.  It  can  be  recrystal- 
lized  from  water.  The  samples  analyzed  were  prepared  under 
widely  varying  conditions. 

Pound.  Calculated  for 

, ' ^  C8CdI8.H20. 


Caesium  ....    20.89  20.75         .  .  .             20.66 

Cadmium    .    .     .     17.13  17.43        17.89            17.39 

Iodine    ....    59.21  59.18         .  .  .             59.16 

Water     ....      2.88  2.80          2.76              2.79 

100.11  100.16                          100.00 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
August,  1893. 

*  Amer.  Jour.  Sci.,  xliv,  230. 


ON  THE  DOUBLE  CHLORIDES,  BROMIDES,  AND 

IODIDES  OF   CAESIUM  AND  ZINC,  AND  OF 

CESIUM  AND  MAGNESIUM.* 

BY  H.  L.  WELLS  AND  G.  F.  CAMPBELL. 

THE  caesium-mercuric  and  the  caesium-cadmium  halides  have 
already  been  studied  in  this  laboratory,  and  it  has  seemed 
desirable  to  extend  the  investigation  to  the  zinc  and  magne- 
sium compounds,  thus  completing  the  study  of  the  caesium 
double  halides  of  this  family  of  bivalent  metals  as  far  as  the 
chlorides,  bromides,  and  iodides  are  concerned. 
We  have  obtained  the  following  salts ; 

3  : 1  Type.  2  :  1  Type.  1  : 1  Type. 

Cs3ZnCl5  Cs2ZnCl4  ? 

Cs3ZnBr5  Cs2ZnBr4  ? 

Cs3ZnI6  Cs2ZnI4  ? 

....  ....  CsMgCl3.6H20 

....  ....  CsMgBr3.6H20 


A  systematic  and  thorough  search  has  been  made  in  all  cases, 
and  it  is  remarkable  that  while  mercury  gave  six  types  of 
caesium  double  salts  and  cadmium  gave  three,  only  two  could 
be  obtained  with  zinc  and  one  with  magnesium.  It  is  evident 
that  the  variety  of  these  double  salts  increases  with  the  atomic 
weight  of  the  bivalent  metal.  The  existence  of  zinc  salts  of 
the  1  :  1  type  is  suspected,  but  the  suspected  products  were 
obtained  only  in  extremely  concentrated  zinc  halide  solutions 
of  such  a  syrupy  nature  that  no  satisfactory  analyses  of  them 
could  be  made. 

The  previously  described  double  halides  of  zinc  and  mag- 
nesium with  the  alkali  metals,  as  far  as  we  have  been  able  to 
find  them,  are  given  in  the  following  table  : 

*  Amer.  Jour.  Sci.,  xlvi,  December,  1893. 


CHLORIDES,   ETC.,   OF  CESIUM  AND  ZINC.          343 

3  : 1  Type.  2  :  1  Type.  1  :  1  Type. 

(NH4)3ZnCl6  (NH4)2ZnCl4  NH4ZnCl8.2H80 

(NH4)2ZnCl4.H20  KZnI8 

Na2ZnCl4.3H20  NaZnI8.liH20 

K2ZnCl4  NaZnF8 

(NH4)2ZnBr4  KZnF8 

(NH4)2ZnI4  NH4MgCl8.6H20 

Na2ZnI4.3H20  NaMgCl8.H2O 

K2ZnI4  KMgCl8.6H20 

K2ZnF4  RbMgCl3.6H2O 

(NH4)2ZnF4.2H20  NH4MgBr8.6H00 

KMgBr8.6H20 

NH4MgI3.6H20 

KMgI3.6H20 

NaMgF3 

There  is  but  a  single  3  :  1  salt,  corresponding  to  our  new 
caesium  compounds  of  that  type.  This  was  described  by 
Marignac.  A  few  1  :  1  zinc  salts  have  been  described,  hence 
it  is  remarkable  that  caesium  zinc  salts  of  this  type  could  not 
be  obtained  in  a  pure  condition,  for  previous  experience  in  this 
laboratory  has  shown  that  caesium  usually  forms  less  soluble 
and  more  stable  double  halides  than  the  other  alkali  metals. 
All  the  previously  described  magnesium  salts  belong  to  the 
1  :  1  type*  to  which  our  caesium  salts  belong,  and  like  the 
latter  nearly  all  have  six  molecules  of  water. 

The  caesium-magnesium  bromide  is  formed  under  narrower 
limits  of  conditions  than  the  chloride,  while  no  iodide  could 
be  prepared,  for  caesium  iodide  crystallized  unchanged  from 
syrupy  solutions  of  magnesium  iodide.  This  behavior  was 
quite  unexpected  in  view  of  the  fact  that  the  ammonium  and 
potassium  double  iodides  are  known,  and  we  have  here  another 
instance  where  caesium,  in  spite  of  its  usual  tendency  to  form 
double  salts,  is  inferior  in  this  respect  to  other  alkali  metals. 
The  idea  suggests  itself  that  great  differences  between  the 

*  Lerch  has  shown  (J.  Pr.  Ch.,  II,  xxviii,  338)  that  the  salts  2KBr.MgBr2. 
6H2O  and  2NH4Br.MgBr2.6H20  of  Lowig  do  not  exist. 


DOUBLE   CHLORIDES,  BROMIDES,   AND  IODIDES 

atomic  weights  of  the  alkali-metal  and  the  less  positive  metal 
are  unfavorable  for  the  formation  of  double  salts,  but  more 
facts  will  be  necessary  in  order  to  establish  such  a  rule. 

The  caesium-magnesium  salts  show  an  increase  in  ease  of 
formation  from  the  iodide  to  the  chloride.  Such  a  gradation, 
both  in  variety  of  salts  and  ease  of  preparation,  is  evident  in 
a  number  of  series  of  double  halides  which  have  been  studied 
in  this  laboratory,  and  the  well-known  tendency  of  fluorides 
to  form  double  salts  indicates  that  the  gradation  probably 
extends  to  these  compounds. 

3  :  1  C  cesium-  Zinc  Chloride,  Bromide,  and  Iodide,  Cs8ZnCl6, 
CszZnBr&,  and  CssZnI6.  —  Each  of  these  salts  crystallizes  in 
colorless  prisms,  apparently  monoclinic  in  form.  They  are 
produced  by  making  aqueous  solutions  of  the  constituents  in 
the  calculated  proportions,  but  in  the  case  of  the  iodide,  with 
these  proportions  the  2  :  1  salt  may  form  if  the  solution  is  too 
dilute.  The  salts  under  consideration  continue  to  form  as  the 
relative  amounts  of  caesium  halides  are  increased  until  the 
latter  crystallize  upon  them.  This  indicates  that  no  double 
salts  with  a  higher  proportion  of  caesium  exist.  The  iodide 
forms  under  rather  wider  limits  of  conditions  than  the  other 
two  salts,  and  it  usually  forms  larger  crystals.  All  the  salts 
require  concentrated  caesium  halide  solutions  for  their  prepara- 
tion, and  the  chloride  especially  is  difficult  to  obtain  in  suffi- 
cient quantity  for  analysis  unless  as  much  as  one  or  two 
hundred  grams  of  the  caesium  halide  is  used.  The  following 
analyses  were  made,  all  of  which  represent  separate  crops  : 


Found. 
_ 

Csesium    .......     62.46         .  .  .  62.20 

Zinc    ........     10.08          9.80  10.13 

Chlorine  .......     27.43        27.34  27.67 


Csesium  . 
Zinc  .  . 
Bromine 


Pound. 

Calculated  for 
Cs3ZnBrfl. 

47.12 

.    .    . 

•     •     . 

46.18 

7.32 

7.54 

7.87 

7.52 

45.91 

46.54 

45.85 

46.30 

OF  CAESIUM  AND  ZINC,  ETC.  345 


Found.  Calculated  for 
• x  Cs8ZnI8. 


Caesium.     .     .     .    36.54        36.20        36.08  36.30 

Zinc  .....      5.77          5.95          5.74  5.92 

Iodine     ....     56.89        57.16         .  .  .  57.78 

2  :  1  Ccesium-Zinc  Chloride,  Bromide  and  Iodide,  Cs2ZnCl4, 
Cs^ZnBr^  and  Cs^Znl^.  —  These  salts  form  colorless  plates,  de- 
creasing in  size  from  the  iodide  to  the  chloride.  They  are  all 
readily  produced  when  larger  proportions  of  the  zinc  halides 
are  used  than  are  necessary  for  the  3  :  1  compounds,  and  they 
recrystallize  from  water  unchanged.  They  continue  to  form, 
through  a  wide  range  of  conditions,  as  more  of  the  zinc 
halides  are  added  until  the  solutions  become  syrupy.  In 
extremely  syrupy  solutions  crystals  of  a  different  appearance 
were  noticed,  but  on  account  of  the  nature  of  these  solutions, 
no  satisfactory  analyses  of  these  products  could  be  made.  It 
seems  probable  that  they  were  1  :  1  salts,  analogous  to  the 
cadmium  salts  of  that  type. 

The  following  analyses  of  separate  crops  were  made  : 

-,  Calculated  for 

Cs2ZnCl4. 

Caesium     .......     55.97        56.09  56.26 

Zinc     ........     13.49        13.87  13.72 

Chlorine  .......    29.89        29.97  30.02 

Calculated  for 
Cs2ZnBr4 

Caesium    .......     40.68         .  .  .  40.86 

Zinc     ........      9.53          9.72  9.98 

Bromine  .......     49.30        49.17  49.16 

Calculated  for 
Found-  Cs,ZnI4. 

Caesium    .......    31.49        31.55  31.70 

Zinc     ........      7.61          7.82  7.75 

Iodine  ........     60.43         .  .  .  60.55 


Ccesium-Magnesium  Chloride  and  Bromide, 
and  CsMgBr^.GH^O.  —  These  salts  form  colorless,  rectangular 
plates  or  flat  prisms  which  are  often  striated.  A  thorough 
search  gave  no  indications  of  salts  of  other  types.  The 


346        CHLORIDES,   ETC.,    OF  CAESIUM  AND  ZINC. 


chloride  is  formed  under  a  wide  range  of  conditions,  the 
bromide  under  a  much  narrower  range,  while  no  double  iodide 
at  all  could  be  prepared. 

The  following  analyses  were  made  of  separate  products : 


Found. 


Calculated  for 


Cs   . 

Mg. 
Cl  . 
H80 


37.14 
680 

.  .  . 

35.66 

683 

35.77 
653 

29.84 

30.13 
30.93 

29.70 

29.55 

28.65 
29.05 

Found. 


Cs    .    .    . 

.     .     27.23 

27.67 

~"* 

Mg  . 

.     .       4.96 

4.50 

5.07 

Br    .     .    . 

.     .     48.93 

48.65 

H20      .     . 

.     .     18.32 

22.33 

Calculated  for 
CsMgBrs.6H20. 

26.32 

4.81 

47.51 

21.37 


It  should  be  mentioned  that  Dr.  H.  L.  Wheeler  of  this 
laboratory  has  attempted  to  prepare  a  double  chloride  of 
caesium  and  beryllium.  He  found  -that  the  simple  salts 
crystallized  side  by  side  from  sufficiently  concentrated  solu- 
tions, and  there  were  no  indications  of  the  existence  of  any 
double  salt,  even  at  rather  low  temperatures.  It  is  therefore 
evident  that  beryllium  follows  the  rule,  already  indicated,  that 
in  this  family  of  bivalent  elements,  Be,  Mg,  Zn,  Cd,  Hg,  the 
tendency  to  form  double  halogen  salts  increases  with  their 
atomic  weights. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
August,  1893. 


ON  THE  C^ESIUM-CUPRIC  CHLORIDES.* 

BY  H.   L.   WELLS  AND  L.   C.  DUPEE. 

As  a  continuation  of  the  work  done  in  this  laboratory  on 
double  halogen  salts,  we  have  taken  up  the  csesium-cupric 
chlorides,  which  had  never  been  thoroughly  investigated.  The 
result  has  been  the  discovery  of  four  double  salts  belonging  to 
three  different  types.  The  beauty  of  the  crystals  in  size  and 
form,  and  the  magnificent  and  unexpected  colors  of  some  of 
them  have  made  the  investigation  a  very  interesting  one.  The 
colors  of  the  anhydrous  salts,  yellow  and  red,  were  perhaps  not 
very  remarkable  since  anhydrous  cupric  chloride  is  reddish 
brown,  but  since  water  of  crystallization  is  supposed  to  give 
green  and  blue  colors  to  cupric  salts,  we  were  considerably 
surprised  to  find  that  a  brown  salt,  CssCuaCl^HaO,  was 
hydrous.  The  color  of  this  hydrous  salt  is,  however,  not 
without  analogy,  for  a  garnet-red,  hydrous  lithium-cupric 
chloride  is  known,  LiCuCl2.2|H2O  according  to  Chassevant,f 
or  LiCuCl8.2H2O  according  to  Meyerhoffer  ;  $  moreover  Engel 
has  described  §  a  garnet-red  compound  HCuCl3.3H2O,  and 
Sabatier's  red  salt  H2CuCl4.5H2O,  ||  is  similarly  exceptional 
in  color. 

In  this  connection  it  should  be  noticed  that  cupric  chloride, 
when  dissolved  in  water  with  an  excess  of  caesium  chloride, 
gives  a  bright  yellow  solution  when  it  is  hot  and  concentrated. 
It  is  well  known  that  solutions  of  cupric  chloride  in  concen- 
trated hydrochloric  acid  have  the  same  yellow  color. 

A  list  of  the  formulas  of  the  salts  to  be  described,  with  their 
colors,  is  given  below.  The  first  salt  has  already  been  de- 
scribed by  Godeffroy.^]" 

*  Amer.  Jour.  Sci.,  xlvii,  Feb.  1894.  t  Compt.  rend.,  cxiii,  646. 

J  Monatshefte,  xiii,  716.  §  Compt.  rend.,  cvi,  273. 

||  Ibid.,  cvi,  1724.  T  Berichte,  viii,  9. 


348  THE   C^ESIUM-CUPRIC  CHLORIDES. 

Cs2CuCl4 Brilliant  yellow. 

Cs2CuCl4.2H2O Bluish  green. 

Cs3Cu2Clr2H20 Brown. 

CsCuClg Garnet-red. 

The  previously  described  cupric  double  halides  containing 
alkali  metals  and  ammonium  belong  to  two  of  the  types  which 
we  have  found  in  investigating  the  caesium-cupric  chlorides. 
A  list  of  all  those  that  we  have  been  able  to  find  is  given 
below.  Four  of  the  double  fluorides  have  been  recently  de- 
scribed by  Von  Helmont.* 

2  :  1  Type.  1  : 1  Type. 

(NH4)2CuCl4.2H20  NH4CuCl3.2H20 
K2CuCl4.2H20  NH4CuF3.2£H20 
K2CuF4  KCuF8 
(NH4)2CuF4.2H20  RbCuF8 
LiCuCl8.2H20 

It  is  to  be  noticed  that  this  list  contains  salts  which  corre- 
spond exactly  to  three  of  the  caesium  compounds,  and  that  the 
group  of  2  :  1  salts  with  two  molecules  of  water  is  a  conspicu- 
ous one. 

The  salt  Cs3Cu2Cl7.2H2O  is  an  interesting  one  because  it 
is  apparently  the  only  known  double  halide  of  an  alkali  metal 
with  a  bivalent  metal,  which  has  the  3  :  2  ratio. 

The  caesium  salts  were  investigated  systematically  by  start- 
ing with  a  solution  of  50  g.  of  caesium  chloride  and  adding  to 
this  from  3  to  5  g.  of  cupric  chloride  at  a  time,  evaporating 
after  each  addition  and  observing  the  products.  At  the  same 
time  another  series  of  experiments  was  made  by  beginning 
with  a  solution  of  50  g.  of  cupric  chloride,  adding  caesium 
chloride  to  this  gradually  and  operating  in  the  same  manner 
as  in  the  other  case.  Many  additional  experiments  were  made, 
sometimes  with  the  use  of  as  much  as  200  g.  of  caesium  chlo- 
ride, and  a  number  of  crystallizations  were  made  in  the  pres- 
ence of  hydrochloric  acid  of  various  strengths.  It  is  believed 

*  Zeitschr.  anorg.  Chem.,  iii,  115. 


THE   CJZSIUM-CUPRIC  CHLORIDES.  349 

that  no  double  salt  capable  of  existence  either  in  warm  solu- 
tions or  at  ordinary  temperatures  has  been  overlooked. 

The  salts  were  so  well  crystallized  and  so  distinct  in  form 
and  color  that  there  was  no  difficulty  in  selecting  pure  products 
for  analysis.  The  usual  precautions,  often  mentioned  in  com- 
munications from  this  laboratory,  were  taken  for  the  removal 
of  mother-liquor  from  the  crystals. 

In  analyzing  the  salts  copper  and  caesium  were  determined 
in  one  portion,  the  first  as  subsulphide,  the  other  as  normal 
sulphate.  The  chlorine  was  determined  in  separate  portions, 
by  the  usual  gravimetric  method. 

Anhydrous  2  :  1  Ccesiurrir  Cupric  Chloride,  Cs2CuCl2.  — 
This  salt,  which  Godeffroy  first  described,  forms  magnificent, 
yellow,  orthorhombic  prisms,  which  were  often  obtained  sev- 
eral centimeters  in  length  and  several  millimeters  in  thickness. 
The  crystals  are  usually  attached  at  one  end,  and  they  often 
arrange  themselves  in  parallel  position,  forming  flat  clusters. 
Doubly  terminated,  short  crystals  were  occasionally  observed. 
Its  formation  was  observed,  with  50  g.  of  caesium  chloride,  in 
the  presence  of  from  5  to  about  25  g.  of  cupric  chloride.  It 
can  be  recrystallized  from  water  if  the  solution  is  made  so  con- 
centrated that  crystals  form  on  cooling,  but  with  more  dilute 
solutions  one  or  both  of  the  hydrous  salts  are  usually  deposited 
on  standing  or  on  spontaneous  evaporation.  The  following 
analyses  represent  different  crops  made  under  considerable 
differences  of  conditions  : 

Found.  Calculated  for 

Cs2CuCl4. 

56.42 
13.46 
30.12 
100.00 


Cs  . 

r 

56.33 

56.14 

56.18 

Cu  . 
Cl  . 

.    .     13.52 
.     .    30.07 

13.45 
29.99 
99.77 

13.47 
30.04 
99.65 

13.48 
30.03 
99.69 

Hydrous  2  :  1  Ccesium-  Cupric  Chloride, 
This  salt  is  bluish  green  in  color,  and  it  loses  its  water  very 
rapidly  on  exposure  to  the  air  with  a  change  of  color  to  bright 
yellow.  It  is  a  well-crystallized,  transparent  salt,  but  its  form 
was  not  made  out  on  account  of  its  instability.  It  is  difficult 


350  THE   CJESIUM-CUPRIC  CHLORIDES. 

to  prepare  it,  at  least  at  summer  temperatures  under  which 
this  investigation  has  been  made,  and  we  have  only  occasion- 
ally observed  it.  It  is  formed  by  allowing  solutions  contain- 
ing nearly  the  required  proportions  of  csesium  and  copper 
chlorides  to  evaporate  spontaneously.  A  sample  quickly 
pressed  on  paper  gave  the  following  analysis : 

,.        .  Calculated  for 

Found.  Cs2CuCl4.2H20. 

Caesium 51.28  52.40 

Copper 12.53  12.50 

Chlorine      28.00 

Water 7.20  7.10 

Another  sample,  which  had  been  exposed  to  the  air  too  long, 
gave  6.02  per  cent  of  water,  and  the  dehydrated  compound 
gave  the  following  analysis : 

Found.  Calculated. 

Cesium 56.09  56.42 

Copper 13.68  13.46 

3  :  2  Ccesium- Cupric  Chloride,  Os3  Ou2  C17.2R2  0.  —  This 
compound  was  obtained  from  solutions  of  nearly  the  required 
proportions  of  csesium  and  cupric  chlorides.  It  usually  forms 
only  at  ordinary  temperatures,  and  if  the  solution  is  too  con- 
centrated, one  or  both  of  the  anhydrous  salts  will  be  deposited 
while  it  is  warm.  The  salt  forms  triclinic  crystals,  often  one 
or  two  centimeters  in  diameter0  The  large  crystals  are  deep 
brown  in  color,  small  ones  and  fragments  are  very  much  paler, 
while  the  powder  is  yellow.  It  is  nearly  stable  at  ordinary 
temperatures,  but  gradually  loses  its  lustre  on  long  exposure. 
All  the  water  goes  off  readily  at  100°.  The  following  analyses 
of  separate  crops  were  made : 

Caesium 
Copper 
Chlorine     . 
Water  .     . 

"  99.54        99.80  100.00 


Found. 

Calculated  for 
Cs8Cu2Cl7.2H2O. 

49.23 

.    .     . 

49.36 

48.96 

15.68 

15.90 

15.74 

15.67 

30.84 

29.90 

30.69 

30.66 

4.22 

4.38 

4.41 

4.44 

THE   C^ESIUM-CUPRIC  CHLORIDES.  351 

1:1  C cesium- Cupric  Chloride,  CsCuClz.  —  This  is  formed 
under  wide  variations  of  conditions,  up  to  the  point  where  the 
solution  is  saturated  with  cupric  chloride.  It  can  be  recrystal- 
lized  from  water.  It  forms  slender  hexagonal  prisms  termi- 
nated by  pyramids.  The  color  is  a  deep  garnet-red,  and  all 
except  very  slender  crystals  appear  black  by  reflected  light. 
The  following  analyses  of  separate  products  were  made : 


Found.  Calculated  for 
• .  CsCuCl,. 


Caesium  .     .     .     43.67  .  .  .         43.58  43.89 

Copper    .    .     .    21.16  21.17        21.06  20.96 

Chlorine      .    .    35.25  35.22        35.00  35.15 

100.08  99.64  100.00 

FIELD  SCIENTIFIC  SCHOOL, 
September,  1893. 


ON  THE  C^ESIUM-CUPRIC  BROMIDES.* 

BY  H.  L.  WELLS  AND  P.  T.  WALDEN. 

WE  have  made  a  systematic  investigation  of  the  caesium- 
cupric  bromides,  following  the  plan,  described  in  the  preced- 
ing article,  which  was  used  for  the  corresponding  chlorides. 
Although  the  work  has  been  very  thorough,  we  have  found 
only  the  following  two  salts  : 

Cs2CuBr4  and  CsCuBr8. 

These  salts  correspond  to  the  two  common  types  of  cupric 
double  halides.  The  fact  that  no  hydrous  salts  could  be 
obtained  was  unexpected,  because  it  has  been  pointed  out  by 
Remsen  f  in  the  case  of  certain  double  halides,  and  it  has  been 
observed  by  one  of  us  in  the  case  of  the  alkaline-lead  halides,  J 
that  the  tendency  to  combine  with  water  seems  to  increase 
with  the  atomic  weight  of  the  halogen.  The  fact  that  hydrous 
double  chlorides  of  caesium  and  copper  exist,  while  no  corre- 
sponding bromides  were  obtained  indicates  that  the  rule  does 
not  apply  in  all  cases. 

2:1  Caesium- Cupric  Bromide,  Cs^CuBr^  — This  compound 
forms  opaque,  black  crystals  having  a  greenish  tint.  The 
powder  is  black.  In  form  and  habit  it  resembles  the  corre- 
sponding chloride  and  is  evidently  orthorhombic  like  that  salt. 
Elongated  prisms,  usually  not  over  5  to  10  mm.  in  length, 
commonly  occurring  in  groups  in  parallel  position,  were 
observed  where  an  excess  of  caesium  bromide  was  used. 
When  the  proportion  of  cupric  bromide  was  increased,  small 
short  crystals  made  their  appearance. 

With  50  g.  of  caesium  bromide  the  compound  is  formed  in 
the  presence  of  from  5  to  about  70  g.  of  cupric  bromide.  The 

*  Amer.  Jour.  Sci.,  xlvii,  February,  1894. 

t  Amer.  Chem.  Jour.,  xiv,  88.  }  Amer.  Jour.  Sci.,  xlvi,  37. 


THE   C^ESIUM-CUPRIC  BROMIDES.  353 

range  of  conditions  under  which  it  is  formed  are  considerably 
wider  than  in  the  case  of  the  corresponding  chloride. 

Of  the  analyses  given  below,  A,  B,  C,  D,  and  E  represent  a 
series  of  preparations  in  which  copper  bromide  was  gradually 
increased  from  5  g.  in  A  to  46  g.  in  E,  while  the  caesium  bro- 
mide remained  constant  at  about  50  g.  and  the  volume  increased 
from  100  c.  c.  in  A  to  150  c.  c.  hi  E.  The  sample  F  was  obtained 
by  recrystallizing  the  salt  from  water,  while  G  resulted  from 
recrystallizing  CsCuBr8. 

Cs.  Cu.  Br. 

A  ....    40.80     .        9.46  49.38=    99.64 

B  .    . 9.68  

C  .     .     .     .    40.75  9.74  48.97=    99.46 

D  .     .     .     .    40.88  9.69  48.95=    99.52 

E  ........  9.78  49.40 

F  .     .     .     .    41.11  9.66  

G 10.00  

Calculated      j  4927-10000 

forCs2CuBrJ4 

1:1  Ccesium-  Cupric  Bromide  Os  CuBrz.  —  This  salt  forms 
short,  hexagonal  crystals  which  are  strung  together  end  to 
end.  They  are  dark  and  opaque,  giving  a  bronze-colored 
reflection,  while  their  powder  is  nearly  black.  When  recrys- 
tallized  from  water,  the  compound  gives  the  2:1  salt,  thus 
differing  from  the  chloride.  It  was  obtained  from  a  solution 
containing  50  g.  of  caesium  bromide  and  70  g.  of  copper  bromide 
with  sufficient  water  to  form  a  volume  of  200  c.c.,  and  it  con- 
tinued to  be  produced  as  cupric  bromide  was  added  until  the 
solution  became  saturated  with  that  compound. 

The  following  analyses  were  made  of  separate  preparations 
which  were  obtained  under  wide  variations  of  conditions. 

Cs     .    . 
Cu     .    .    . 
Br     .     .    . 

99.74      99.14  100.20          100.00 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
September,  1893. 

23 


Found. 

Calculated 
for  CsCuBr 

29.93 

29.09 

.  .  .       30.43 

30.48 

14.72 

15.09 

14.73      14.81 

14.53 

55.09 

54.96 

.  .  .       64.96 

54.99 

ON  THE  CAESIUM-CUPROUS  CHLORIDES.* 

BY  H.  L.  WELLS. 

THE  salts  to  be  described  were  prepared  by  heating  solutions 
containing  caesium  chloride  and  cupric  chloride  with  copper 
wire,  and  sufficient  hydrochloric  acid  to  prevent  the  formation 
of  basic  salts ;  then,  after  the  copper  in  solution  was  chiefly  in 
the  form  of  cuprous  chloride,  cooling  to  crystallization. 

When  the  solutions  were  dilute,  caesium  chloride  being  in 
excess,  very  slender  white  prisms  were  obtained  under  wide 
variations  of  conditions.  The  crystals  became  yellowish  while 
being  dried  with  paper,  but  they  were  apparently  nearly  stable 
in  the  air  when  dry.  It  was  found  that  the  salt  was  decom- 
posed by  water.  Two  different  products  were  analyzed. 

•ipnnni  Calculated  for 

ound>  CsCl.CuzCl2. 

Caesium 36.93        36.36  36.29 

Copper 34.33        34.17  34.64 

Chlorine      ....    28.95        28.87  29.07 

The  results  show  that  the  formula  CsCu2Cl3  belongs  to  this 
salt. 

On  using  more  concentrated  solutions,  also  with  an  excess 
of  caesium  chloride,  thin,  rectangular,  colorless  plates  were 
produced,  sometimes  10  or  20  mm.  in  diameter.  The  range  of 
conditions  under  which  this  salt  is  produced  is  wide,  and  large 
crops  of  it  are  easily  prepared.  As  the  concentration  of  the 
caesium  chloride  solutions  was  increased,  the  same  compound 
appeared  in  the  form  of  blade-like  crystals  with  pointed  ends. 
By  dissolving  this  salt  in  water  the  previously  described  com- 
pound is  produced  by  crystallization.  The  surface  of  the 
crystals  becomes  yellow  on  drying,  but  when  dry  it  appears  to 

*  Amer.  Jour.  Sci.,  xlvii,  February,  1894. 


THE   CAESIUM-CUPROUS   CHLORIDES.  355 

be  very  stable.  The  first  two  analyses  represent  separate 
crops  of  the  rectangular  plates,  the  third  a  crop  of  the  blade- 
like  crystals. 

Found. 


Caesium 
Copper  . 

i. 
....     56.81 
....     17.95 

n. 
56.66 
1789 

m. 
56.84 
17.84 

uaicuiatea  xor 
SCsCl.CujClj. 

56.72 
1805 

Chlorine 

....    25.03 

25.08 

25.13 

25.23 

It  is  evident  that  this  salt  has  the  formula  Cs8Cu2Cl6. 

With  nearly  or  quite  saturated  caesium  chloride  solutions 
containing  comparatively  little  cuprous  chloride,  prismatic 
crystals  are  formed  on  cooling.  The  crystals  are  very  pale 
yellow  in  color,  and  their  lustre  is  less  brilliant  than  that  of 
the  preceding  compound.  Crystals  having  a  diameter  of  two 
or  three  millimeters  and  a  length  of  several  centimeters  were 
sometimes  observed.  This  salt  forms  under  very  narrow  limits 
of  conditions,  and  it  is  very  difficult  to  obtain  it  free  from  the 
preceding  salt,  and  especially  from  caesium  chloride,  which 
usually  crystallizes  with  it  when  the  conditions  are  right  for 
its  formation.  After  a  great  many  trials  three  crops  which 
were  satisfactory  were  obtained  for  analysis.  The  third  anal- 
ysis represents  crystals  which  were  picked  out  of  the  solution 
one  at  a  time  and  separately  pressed  between  smooth  filter- 
papers.  All  the  preparations  were  carefully  examined  under 
the  microscope  and  were  evidently  pure. 

Found.  Calculated  for 

, • v        6CsCLCu2Clr2HjO. 


Caesium 64.77  65.07  64.09  64.10 

Copper 9.38  9.42  10.04  10.20 

Chlorine 22.70  22.83  .  .  .  22.81 

Water  (difference)    .  3.15  2.69        3.14  2.89 

The  analyses  show  that  the  salt  has  the  formula  Cs8CuCl4. 
H2O. 

The  previously  described  cuprous  double  halogen  salts,  with 
the  new  caesium  salts  for  comparison,  are  given  below : 


356  THE   CAESIUM-CUPROUS   CHLORIDES. 

Csesium  Salts.  Previous  Salts. 

CsCl.Cu2Cla  4NH4C1.3Cu,Cl, 
3CsCl.Cu,Cl,  2NH4I.Cu2I2.H20 
6CsCl.Cu2Cl2.2H20  4KCl.Cu2Cl2 
4NH4Cl.Cu2Cl2 

It  is  remarkable  that  there  is  no  correspondence  in  type 
between  the  caesium  compounds  and  the  others,  and  that  such 
a  variety  of  types  appears  to  exist.  The  formula  4NH4C1. 
3Cu2Cla  may  be  considered  somewhat  doubtful  on  account  of 
its  complex  ratio,  and  because  with  one-fourth  less  ammonium 
chloride  it  would  correspond  to  the  first  caesium  salt. 

The  salt  Cs3Cu«Cl6  is  noticeable  on  account  of  its  rather 
complex  formula  and  because  it  has  the  same  ratio  of  caesium 
to  copper  as  the  previously  described  cupric  salt  Cs3Cu2Cl7. 
2H2O.  Since  the  latter  has  a  ratio  that  is  unique  among  the 
bivalent  metal  double  halogen  salts,  a  close  structural  relation 
between  the  two  compounds  is  suggested. 

These  caesium-cuprous  chlorides  show  a  decided  lack  of  con- 
formity with  Remsen's  law*  concerning  the  composition  of 
double  halides.  Two  out  of  three  of  them  fail  to  correspond 
to  the  law,  while  one  of  these,  instead  of  not  containing  more 
than  one  CsCl  for  one  CuCl,  actually  contains  three  times  as 
much  caesium  chloride  as  Remsen's  law  allows. 

My  thanks  are  due  to  Mr.  L.  C.  Dupee,  who  prepared  and 
analyzed  one  sample  of  the  salt  CsCu2Cl3. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
September,  1893. 

*  Amer.  Chem.  Jour.,  xi,  296 ;  xiv,  85. 


ON  THE  DOUBLE  CHLOEIDES  AND  BROMIDES  OF 
CAESIUM,  RUBIDIUM,  POTASSIUM,  AND  AMMO- 
NIUM WITH  FERRIC  IRON,  WITH  A  DESCRIPTION 
OF  TWO  FERRO-FERRIC  DOUBLE  BROMIDES. 

BY  P.  T.  WALDEN. 

PREVIOUS  investigation  on  the  double  ferric  halides  seems 
to  have  been  devoted  exclusively  to  the  chlorides,  and  the 
metal  caesium  has  not  as  yet  been  worked  with  in  this 
connection. 

In  view  of  these  facts  it  appeared  desirable  to  prepare,  as 
far  as  possible,  a  complete  series  of  the  double  halogen  salts 
of  the  above-named  metals.  Only  negative  results  were 
obtained,  however,  when  attempts  were  made  to  prepare 
double  iodides,  so  that  the  work  was  necessarily  confined  to 
the  chlorides  and  bromides. 

The  following  compounds  have  been  previously  described : 

Rb8FeCl,j  K2Fe016H20 

....  (NH4)2FeCl6H20 

....  Na2FeCl6H20 

The  existence  of  the  above  potassium  and  ammonium  salts 
has  been  confirmed  in  the  present  investigation,  but  the  com- 
pound Rb8FeCl«,  described  by  Godenroy,t  could  not  be  made, 
although  a  hydrous  salt  of  the  same  type  was  prepared  with 
caesium.  A  most  careful  series  of  experiments  using  large 
quantities  of  the  constituent  chlorides  was  made  in  the 
attempt  to  prepare  the  rubidium  salt  just  mentioned.  It  is 
not  believed  to  be  possible  that  Godeffroy  obtained  this  com- 
pound, and  his  error  was  probably  due  to  his  neglecting  the 

*  Amer.  Jour.  Sci.,  xlviii,  October,  1894. 
t  Arch.  Pharm.  [3],  ix,  343. 


358       DOUBLE   CHLORIDES  AND  BROMIDES,  ETC., 

water  of  crystallization  in  the  salt  Rb2FeCl6H2.  There  is  not 
a  great  difference  between  the  theoretical  composition  required 
by  a  3  :  1  anhydrous  compound  and  the  2  :  1  salt  with  one 
molecule  of  water,  especially  as  far  as  the  chlorine  and  iron 
are  concerned.  This  can  be  seen  from  the  following  com- 
parison: 

Calculated  for  Calculated  for 

RbsFeCle.  Rb2FeCl5H2O. 

Eubidium     .    .     .    48.83  40.44 

Iron 10.65  13.29 

Chlorine  ....    40.52  42.01 

Water      ....  __L_L_L_  4.26 

100.00  100.00 

Since  the  hydrous  2  :  1  salt  is  easily  prepared,  it  therefore 
seems  certain  that  this  must  have  been  the  single  salt  de- 
scribed by  Godeffroy. 

The  following  is  a  list  of  the  salts  obtained  : 

3  :  1  Type.  2  :  1  Type.  1  :  1  Type. 

Cs8FeCl6.H2O  Cs2FeCl5.H20  CsFeCl44H20 

Cs2FeBr5.H2O  CsFeBr4 

Kb2FeCl6.H2O  

Eb2FeBr6.H20  

K2FeCl6.H20*  


(NH4)2FeCl6.H20*     

NH4FeBr4.2H20 

It  will  be  noticed  that  the  type  2  :  1  is  the  most  frequently 
recurring,  being  found  in  every  case  except  with  potassium 
and  ammonium  bromides.  The  salts  of  this  type,  as  might  be 
expected,  are  also  the  most  stable  and  easily  made,  especially 
with  caesium  chloride,  where  it  is  formed  through  a  very  wide 
range  of  conditions,  leaving  only  a  narrow  margin  for  the  other 
two  members  of  the  series.  It  is  remarkable,  in  view  of  these 
facts,  that  this  type  should  not  have  been  obtained  with 

t  These  two  salts  have  been  previously  described  by  Fritzsche,  J.  prakt 
Chem.,  xviii,  483. 


WITH  FERRIC  IRON.  359 

ammonium  bromide,  while  the  1  :  1  type,  which  is  compara- 
tively unstable  in  other  cases,  is  made  without  difficulty. 

This  investigation  furnishes  another  striking  example  of  the 
fact,  already  noticed  several  times  in  this  laboratory,  that 
caesium  halides  form  more  complete  series  of  double  salts  than 
the  halides  of  the  other  alkali  metals.  With  caesium  chloride 
we  get  a  complete  series,  while  with  the  chlorides  of  the 
other  alkali  metals  only  one  type  appears.  In  the  bromides 
no  double  ferric  potassium  salt  could  be  isolated,  whereas  two 
well-defined  and  comparatively  stable  compounds  were  ob- 
tained with  caesium. 

Wells  and  Campbell  *  have  called  attention  to  the  fact  that, 
in  a  number  of  cases,  double  halides  show  an  increase  in  ease 
of  formation  from  the  iodides  to  the  chlorides.  No  better 
illustration  could  be  had  of  this  truth  than  the  series  of  salts 
prepared  in  the  present  investigation,  where  the  chlorides  were 
made  in  greater  number  and  with  more  ease  than  the  bromides, 
while  no  iodides  at  all  could  be  obtained. 

Preparation.  —  All  these  salts  were  made  by  mixing  solu- 
tions of  the  simple  halides,  evaporating  and  cooling  to  crystal- 
lization. It  was  found  necessary  in  all  cases  to  use  solutions 
slightly  acidified  with  the  corresponding  halogen  acid,  in  order 
to  prevent  the  formation  of  basic  salts.  A  record,  as  nearly 
exact  as  possible,  was  kept  of  the  relative  quantities  of  the 
constituents  used,  and  this  has  been  indicated  under  each  salt. 
The  crystals  were  freed  from  the  mother-liquor  by  pressing 
between  smooth  filter  papers,  and  in  every  case  where  it  was 
admissible  they  were  further  dried  by  exposure  to  the  air  of 
the  laboratory.  Where  the  salt  was  at  all  deliquescent  it  was 
at  once  removed  to  a  tightly  stoppered  tube  whose  weight  had 
been  previously  determined  and  weighed  without  loss  of  time. 
In  this  manner  a  quite  unstable  body  could  be  analyzed  and 
satisfactory  results  obtained.  The  purity  of  all  the  simple 
alkali  halides  was  tested  with  the  spectroscope  before  using. 
The  very  pure  rubidium  chloride  used  for  this  work  was  fur- 
nished to  this  laboratory  for  the  encouragement  of  scientific 

*  Amer.  Jour.  Sci.,  HI,  xlvi,  432. 


360      DOUBLE  CHLORIDES  AND  BROMIDES,  ETC., 

investigation  by  the  firm  of  E.  Merck  of  Darmstadt,  through 
their  agents,  Messrs.  Merck  &  Co.  of  New  York,  and  our 
thanks  are  due  to  them  for  their  unsolicited  generosity. 

Method  of  Analysis.  —  Iron  was  weighed  as  Fe2O3  in  all 
cases,  after  having  been  separated  from  the  alkali  metal  by 
precipitation  with  ammonia.  The  filtrate  from  this  precipita- 
tion was  evaporated  to  dryness,  the  alkali  metal  converted  into 
sulphate  and  weighed  as  such  after  ignition  in  a  stream  of  air 
containing  ammonia.  Ammonium  was  estimated  by  distilling 
with  a  solution  of  potassium  hydroxide,  absorbing  the  NH8  liber- 
ated in  hydrochloric  acid  and  determining  its  amount  by  alka- 
limetry. Water  was  determined  by  combustion  behind  sodium 
carbonate  and  absorption  in  a  washed  calcium  chloride  tube. 
With  (NH4)2FeCl6H2O  the  water  was  removed  by  subjecting 
the  salt  to  a  temperature  of  150°  C.  in  an  air  bath  for  one  hour. 

The  Double  Chlorides.  —  These  salts  are  all  red  except 
CsFeCl4jH2O,  which  is  straw  yellow.  There  is  a  distinct 
gradation  in  the  shades  of  the  salts  of  the  type  2  :  1  from 
(NH4)2FeCl6H2O,  which  is  a  deep  ruby  red,  growing  lighter 
through  the  caesium,  rubidium,  and  potassium  compounds  until 
the  last  is  very  nearly  the  color  of  potassium  dichromate. 

3:1  Ccesium  Ferric  Chloride,  CssFeCl6H20.  —  This  salt  is 
the  only  one  of  the  3  :  1  type  which  was  prepared  in  the 
present  investigation.  It  separated  from  a  solution  containing 
50  g.  of  caesium  chloride  and  from  .5  g.  up  to  2.5  g.  of  ferric 
chloride.  The  following  analyses  were  made  from  separate 
crops : 


Found>  Calculated  for 


Caesium  .  .  . 
Iron  .... 

A. 

.     58.30 
791 

a 
58.42 
785 

c. 

CssFeCl«H2O. 

58.17 
£  17 

Chlorine  .  . 
Water  .  .  . 

.    30.87 
.      2.74 

30.82 
2.72 

30.98 
2.64 

31.01 
2.65 

99.82        99.81  100.00 


In  color  it  closely  resembles  sodium  dichromate.  It  is  well 
crystallized  in  small  prisms  which  are  arranged  in  compact 
clusters  radiating  from  a  centre. 


WITH  FERRIC  IRON. 


361 


2  : 1  Ccesium,  Rubidium,  Potassium,  and  Ammonium  Fer- 
ric Chlorides,  CszFeOl,HzO,  Eb2FeCl5H,0,  K2FeCl6H20,  and 
(NH<\FeCl&H20.  —  Ii  solutions  of  the  several  alkali  chlo- 
rides containing  50  g.  each  be  made,  it  is  necessary  to  add 
3  g.  of  ferric  chloride  to  make  the  caesium  salt  of  this  type, 
10  g.  to  make  the  rubidium  salt,  15  g.  to  make  the  potassium 
salt,  and  70  g.  to  make  the  ammonium  salt.  The  caesium, 
rubidium,  and  potassium  compounds  can  be  recrystallized 
unchanged,  although  with  the  last  two  there  is  a  tendency  to 
separate  simple  alkaline  chlorides  at  the  same  time.  Several 
separate  crops  were  analyzed  of  each  salt  with  the  results 
shown  below: 


Caesium  .    . 
Iron  .     • 

rouna. 

-«- 

Calculated  for 

.     .     51.15 
.     .     11.05 

B. 

51.05 
10.98 
34.19 
3.59 

c    *             CsjFeCl5HjO. 
51.40 

10.82 
34.02            34.30 
3.48 

Chlorine 
Water     .    . 

Rubidium    . 
Iron   . 

.     .    34.36 
.     .      3.55 

100.11 

Foi 
A. 

.     .     40.51 
.     .    13.28 

99.81 

and. 
B. 

40.69 
13.33 
41.92 
4.20 

100.00 

Calculated  for 
Bb,FeCl6H20. 

40.44 

13.29 
42.01 
4.26 

Chlorine 
Water    .     . 

Potassium  . 

.    .    41.91 
.    .      4.23 

99.93 

Foi 
A. 

.     .    23.66 
.    .     16.86 

100.14 

and. 
B. 

23.54 

16.99 
53.35 
5.96 

100.00 

Calculated  for 
K,FeCl8HjO. 

23.73 

16.98 
53.84 
5.45 

Chlorine 
Water    .     . 

Ammonium 

.    .    53.56 
.     .      6.20 

100.28 

99.84 

Pound. 

100.00 

Calculated  for 

A. 

.     .    12.39 
.    .    19.13 

B. 

12.36 
18.95 
61.07 
•  *  • 

c      *           (JNH4)2Fe018HsO. 

12.00            12.52 
19.48 
61.22            61.74 
6.26 

Chlorine 
Water    .     . 

.    .    61.21 
.     .      7.39 

100.12 

100.00 

362      DOUBLE   CHLORIDES  AND  BROMIDES,   ETC., 

All  these  salts  are  well  crystallized  in  short  prisms.  The 
caesium  and  rubidium  compounds  are  permanent  in  the  air,  but 
the  potassium  and  ammonium  salts  absorb  moisture  quite 

rapidly. 

1:1  Ccesium  Ferric  Chloride,  CsFeCl^.\HzO.  —  This  was 
made  from  a  solution  containing  50  g.  of  caesium  chloride  and 
180  g.  of  ferric  chloride.  Below  are  the  analyses  of  separate 
crops : 

Found-  Calculated  for 


Caesium  . 

A. 

.    .     .    38.39 
.    .    .    17.03 

B. 

38.53 
16.85 

c. 

CaFeCUiB 

39.39 
16.48 

Chlorine 
Water  . 

.    .    .    41.76 
.    .     .      3.14 

41.73 
3.63 

41.98 
4.03 

41.77 
2.36 

100.32 

100.74 

100.00 

This  salt  absorbs  moisture  in  the  air  so  rapidly  that  con- 
siderable difficulty  was  experienced  in  preparing  samples  for 
analysis.  It  is  regarded  as  containing  half  a  molecule  of  water 
on  the  evidence  of  the  analytical  results,  although  it  is  not 
unreasonable  to  suppose  that  all  the  water  found  was  absorbed, 
especially  as  the  bromide,  CsFeBr4,  is  anhydrous.  The  crys- 
tals were  slender  needles,  which  rapidly  lost  their  yellow 
color  in  the  air,  turning  red. 

The  Double  Bromides.  —  These  are  all  very  dark  green, 
almost  black  and  quite  opaque.  Like  the  chlorides,  the  2 :  1 
caesium  salt  is  darker  than  the  rubidium  compound  of  the 
same  type.  As  no  corresponding  potassium  or  ammonium 
salt  could  be  made,  the  comparison  can  be  carried  no  farther. 
The  caesium  and  ammonium  1 :  1  bromides  are  of  nearly  the 
same  color.  None  of  the  double  bromides  are  capable  of 
recrystallization. 

#  :  1  Ccesium  and  Rubidium  Ferric  Bromides,  Cs^FeBr^O 
and  Kb2FeBrBH20.  —  The  first  of  these  salts  was  made  with 
the  quantities  of  the  constituent  bromides  about  equal,  the 
second  with  50  g.  of  rubidium  bromide  to  60  g.  of  ferric 
bromide.  The  following  are  the  analyses: 


WITH  FERRIC  IRON. 


363 


Caesium  .    . 

Found. 
A.                    B. 

.     .    .    35.76        35.60 

Iron        . 

.    .     .      8.05          7.93 

Bromine 
Water     .    . 

.     .    .     54.20        54.15 
.     .    .      2.52          2.84 

Eubidium   . 
Iron   . 

100.53      100.52 

Found. 
A.                   B. 

...     26.20        26.14 
.    .     .      8.86          8.99 

Bromine 
Water     .     . 

.     .     .    62.13        62.12 
.    .    .      2.90          2.88 

100.09      100.13 

Calculated  for 


35.95 
7.56 

54.05 
2.44 

100.00 

Calculated  for 


26.51 

8.68 

62.02 

2.79 
100.00 


Both  compounds  were  obtained  in  short  doubly  terminated 
prisms.  The  caesium  salt  is  comparatively  stable,  while  the 
rubidium  salt  decomposes  rapidly  in  the  air. 

1:1  Ocesium  and  Ammonium  Ferric  Bromides,  CsFeBr^ 
and  NHiFeBr4£H2  0.  —  A  solution  of  50  g.  of  caesium  bromide 
and  100  g.  of  ferric  bromide  gave  the  first  of  these  salts  in 
slender  needles.  The  second  could  not  be  obtained  until 
250  g.  of  ferric  bromide  had  been  added  to  50  g.  of  ammo- 
nium bromide.  Separate  crops  of  each  were  analyzed  with  the 
results  given  below. 

Found.  Calculated  for 


Csesium  . 

.     .    26  02 

Iron  .     .     .     . 

.     .    11.25        11  30 

Bromine      .    . 

.     .    63.01        62.99 

100.28 

Found. 

Ammonium  .     . 
Iron          .    .     , 

A.                      B. 

.      3.98          3.92 
.    13  48        13  59 

c. 
3.83 

Bromine  .     .     . 
Water      .    .    . 

.    74.85        74.71 
.      7.69*        7.78* 

•       •      0 

•    •    • 

100.00      100.00 

Calculated  for 


4.19 
13.02 
74.42 

8.37 
100.00 


*  Water  by  difference. 


364      DOUBLE  CHLORIDES  AND  BROMIDES,  ETC., 

As  the  ammonium  salt  is  so  deliquescent  that  no  satisfactory 
determination  of  water  was  possible,  it  was  taken  by  difference, 
and  it  is  believed  that  the  results  warrant  the  acceptance  of 
the  formula  as  written  above.  Great  care  was  exercised  in  an 
attempt  to  prepare  a  2  :  1  ammonium  bromide,  but  without 
success.  NH4FeBr42HaO  and  simple  ammonium  bromide  were 
finally  crystallized  out  together  in  the  same  solution.  This  is 
regarded  as  good  evidence  that  no  salt  of  a  type  higher  in 
ammonium  exists. 

Ferro-ferric  Salts:  ElBr.FeBr^FeBrz.3HzO  and  KBr.FeBr* 
%FeBrz3HzO. — While  endeavoring  to  obtain  a  double  ferric 
bromide  with  potassium,  a  dark  green  body  separated  from 
a  solution  containing  an  excess  of  bromine,  which  gave  a 
black  hydroxide  with  ammonia.  This  was  considered  so 
remarkable  that  an  effort  was  made  to  prepare  corresponding 
salts  with  the  other  alkali  halides  and  ammonium,  under  the 
same  conditions.  This  attempt  resulted  in  the  formation  of 
only  one  other  compound  of  the  same  kind,  that  with  rubidium. 
The  ferrous  iron  in  those  salts  was  determined  by  titration 
in  the  presence  of  hydrochloric  acid  with  a  standard  potassium 
dichromate  solution.  It  was  found  to  be  impossible  to  deter- 
mine water  satisfactorily  on  account  of  the  extreme  instability 
of  both  salts.  It  was  therefore  taken  by  difference.  The 
rubidium  salt  resulted  from  the  bringing  together  in  solution 
of  50  g.  of  rubidium  bromide  and  150  g.  of  ferric  bromide,  the 
potassium  salt  from  a  solution  of  50  g.  of  potassium  bromide 
and  250  g.  of  ferric  bromide.  Below  are  the  analytical 
results,  A,  B,  and  C  being  separate  crops. 

Found. Calculated  for 

r~~^~         ~~£ —          — ^     RbBr.FeBr2.2FeBr.3H20. 

Eubidium  .    .    .      7.25  8.32 

Ferrous  iron  .     .      5.17  5.16         5.53  5.45 

Ferric  iron     .     .     11.10  10.71       10.13  10.90 

Bromine    .     .     .     68.83  68.37       68.48  T0.07 

Water  .         .    .      7.65*  5.26 

100.00  100.00 

*  Water  by  difference. 


WITH  FERRIC  IRON.  365 


Found. 


Calculated  for 
KBr.FeBr,.2FeBr3.3H,O. 

Potassium 3.47  3.92  3.98 

Ferrous  iron  ....      4.31  4.26  5.71 

Ferric  iron     ....     12.36  11.70  11.42 

Bromine 73.15  73.09  73.39 

Water 6.71*  .  .  .  5.50 

100.00  100.00 

These  salts  are  dark  green  in  color  and  quite  opaque,  like 
the  double  ferric  bromides  described  above.  The  crystalliza- 
tion of  the  rubidium  salt  is  apparently  rhombohedral,  that  of 
the  potassium  cubical. 

In  conclusion  the  author  wishes  to  express  his  sincere  thanks 
to  Prof.  H.  L.  Wells,  under  whose  direction  the  work  has  been 
carried  on,  for  his  kindly  aid  and  many  valuable  suggestions. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
July,  1894. 

*  Water  by  difference. 


ON  THE  CESIUM-COBALT  AND  CAESIUM-NICKEL 

DOUBLE  CHLORIDES,  BROMIDES, 

AND  IODIDES. 

BY  G.  F.  CAMPBELL. 

As  a  continuation  of  the  work  in  this  laboratory  on  double 
halogen  salts,  the  investigation  of  the  above-mentioned  com- 
pounds has  been  taken  up.  The  study  has  been  made  in  a 
systematic  manner  with  the  view  of  preparing  as  complete  a 
series  as  possible.  The  salts  obtained  belong  to  three  types, 
and  are  as  follows: 

3  : 1  Type.  2  : 1  Type.  1  : 1  Type. 

Cs8CoCl6  Cs2CoCl4  CsCoCl8.2H20 

Cs8CoBr5  Cs2CoBr4  

....  Cs2CoI4  

....  ....  CsNiCls 

....  ....  CsNiBr3 

The  results  show  that  cobalt  forms  double  salts  with  much 
greater  facility  than  nickel,  for  with  the  latter  metal  only  the 
chloride  and  bromide  of  a  single  type  could  be  obtained. 

The  series  illustrates  the  increase  in  ease  of  formation  of 
double  salts  from  the  iodides  to  the  chlorides,  which  has  been 
previously  observed,  especially  in  the  case  of  the  csesium-mag- 
nesium  salts  by  Wells  and  Campbell.*  No  csesium-nickel 
iodide  could  be  prepared. 

It  should  be  noticed  that  the  two  salts  of  the  3  :  1  type  are 
exceptions  to  Remsen's  law  concerning  this  class  of  bodies. 

The  previously  described  double  halogen  salts  of  cobalt  and 
nickel,  as  far  as  I  have  been  able  to  learn,  correspond  to  two 
types  of  the  caesium  salts,  and  are  as  follows  : 

*  Amer.  Jour.  Sci.,  xlviii,  November,  1894.  t  Ibid.,  xlvi,  432. 


DOUBLE   CHLORIDES,  BROMIDES,  AND  IODIDES.       367 


2  : 1  Type. 

(NH4)2CoF4.2H20 
(NH4)2NiF4.2H20 


1  : 1  Type. 

NH4CoCl8.6H20 

NH4NiCl8.6H20 

KCoF8.H2O 

KNiF8.H20 

NaCoF8.H20 

NaNiF8.H20 


The  following  table  gives  approximately  the  composition  of 
the  solutions  from  which  the  caesium  salts  under  consideration 
were  crystallized  by  concentration  and  cooling : 


Cs  :  Co  or  Ni  (Atoms.) 


Cs3CoCl5      .    ,     . 

From  12 

1 

Cs2CoCl4     . 

"       6 

1 

CsCoCl3.2H20  .    . 

«       0.4 

1 

Cs3CoBr5     .     .     . 

"       2 

1 

Cs2CoBr4     .     .     . 

"       1 

1 

Cs2CoI4  ,    .    .    . 

«       1 

4 

CsNiClg       .     .    . 

"     12 

1 

CsNiBr8.     .     .     . 

"       2.5 

1 

bo     6:1 
«  0.4  :  1 

1  "  syrupy  solution  of  CoCl2 
"1:1 

"  syrupy  solution  of  CoBr2 
«  1  :  16 

"  syrupy  solution  of  NiCl2 
"  syrupy  solution  of  NiBr2 


More  or  less  of  the  corresponding  halogen  acid  was  present 
in  each  case,  and  an  increase  of  this  was  apparently  equivalent 
in  effect  to  the  addition  of  the  caesium  halide.  In  the  case  of 
the  two  nickel  salts,  a  rather  large  amount  of  the  acid  was 
desirable,  for  if  it  was  not  present,  the  salts  appeared  only 
upon  heating  the  concentrated  solutions  and  dissolved  when 
they  cooled. 

The  color  of  the  chlorides  containing  cobalt  is  a  magnificent 
blue,  the  bromides  and  the  iodides  containing  the  same  metal 
are  green,  while  the  two  nickel  salts  are  yellow.  The  two 
nickel  salts  form  almost  microscopic  crystals.  The  two  salts 
of  the  3 :  1  type  were  obtained  in  crystals  having  a  diameter  of 
about  5  mm.,  apparently  combinations  of  the  cube  and  octahe- 
dron. The  salts  of  the  2  : 1  type  form  large  plates  or  prisms, 
the  habit  evidently  depending  upon  the  composition  of  the 
solutions  from  which  they  crystallize.  The  salt  CsCoCl8.2H2O 
forms  rather  small  plates.  Besides  the  blue  salt  just  men- 


368          CESIUM-COBALT  AND   CAESIUM-NICKEL 


tioned,  a  red  csesium-cobalt  chloride  of  the  1  :  1  type  was 
obtained  which  lost  water  of  crystallization  so  readily,  with 
change  of  color,  that  it  could  not  be  analyzed  in  its  original 
condition. 

The  compound  Cs2CoI4  is  deliquescent,  while  the  other  salts, 
here  described,  are  stable.  All  the  salts  are  whitened  when 
brought  into  contact  with  water  or  alcohol,  evidently  on 
account  of  decomposition. 

The  following  analyses  were  made : 


Found    .    . 
Calculated  . 


CsaCoCl5. 

Caesium. 

62.79 
62.82 


Cobalt. 

9.16 
9.24 


Chlorine. 

27.83 

27.74 


Found    . 
Calculated 


Caesium. 

56.86 
56.99 


Cobalt. 

12.53 
12.58 


Chlorine. 

30.40 
30.43 


Found     . 
Calculated 


Caesium.  Cobalt. 

38.64        17.67 
39.80        17.56 


Chlorine.  Water. 

32.07        10.94 
31.87        10.77 


Found  A     . 
«     B 

.  .  .  46.65 

"     C     . 

Calculated  . 

.  .  .  45.81 
.  .  .  46.52 

Cobalt. 

6.88 
7.44 
7.08 
6.84 


Bromine. 

46.33 
46.97 
46.52 
46.64 


Found  A 
"  B 
"  C 

Calculated 


Caesium. 

41.21 


41.26 


Cobalt. 

9.49 
9.20 
9.25 
9.10 


Bromine. 

49.43 
49.60 
49.32 
49.64 


DOUBLE   CHLORIDES,  BROMIDES,  AND  IODIDES.       369 


Found  A 
"  B 
«  C 

Calculated 


Found  A 
"      B 
Calculated 


Found  A 
"      B 

Calculated 


Caesium. 

29.69 


31.93 


44.42 

44.61 

CsNiBrs. 

Caesium. 

29.93 
30.60 
30.81 


Cobalt. 
7.10 

7.34 
7.31 
7.09 


Nickel. 
19.70 

19.14 
19.66 


Nickel. 

13.83 
13.58 
13.58 


Iodine. 
60.24 

60.29 
60.98 


Chlorine. 

35.78 
35.57 
35.73 


Bromine. 

55.84 
55.49 
55.61 


The  author  takes  pleasure  in  expressing  his  indebtedness  to 
Prof.  H.  L.  Wells  for  valuable  advice  in  connection  with  this 
investigation. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
September,  1894. 


24 


ON    THE    DOUBLE    HALIDES    OF    CESIUM, 

RUBIDIUM,   SODIUM,  AND   LITHIUM 

WITH  THALLIUM.* 

BY  J.   H.  PRATT. 

IN  previous  investigations  upon  the  double  halides  of  triva- 
lent  thallium  with  the  alkali  metals,  the  salts  of  only  potassium 
and  ammonium  seem  to  have  been  carefully  studied.  The 
only  caesium  and  rubidium  salts  that  have  been  made  are 
Cs8TlC1.2H2O  and  Rb8TlCl6.2H2O  described  by  Godfrey,* 
but  in  the  present  investigation  the  compounds  of  this  type 
were  found  to  have  one  instead  of  two  molecules  of  water  of 
crystallization. 

The  present  research  has  been  carried  out  very  carefully 
and  systematically  in  order  to  obtain  as  complete  a  series  of 
double  salts  in  each  case  as  possible.  The  salts  that  have 
been  made  belong  to  four  types,  corresponding  to  those  pre- 
viously made  with  potassium  and  ammonium,  and  are  as 
follows : 

3:1  2:1  3:2  1:1 

Cs,TlCl..H,0  Cs2TlC]6  Cs3Tl2Cl9  

Cs2TlCl6.H20          

Cs3Tl2Br9  CsTlBr4 

CsTlI4 

Kb8TlCl6.H20  Eb2T1015.H20         

Kb8TlBr6.H20  KbTlBr4.H20 

KbTlI4.2H20 

Na8TlCl6.12H20  

Li8TlCl6.8H20  

For  comparison,  a  list  of  the  previously  described  double  salts 
with  potassium  and  ammonium  is  also  given. 

*  Amer.  Jour.  Sci.,  xlix,  May,  1895.        f  Landenberg's  Handworterbuch. 


DOUBLE  HALIDES   WITH  THALLIUM.  371 

3:1  2:1                          3:2                          1:1 

K8T1C16.2H20  K2T1C16.3H20  K8T12C19.1^H20    KTlBr4 

(NH4)8T1C16.2H20 K8Tl2Br9.liH20   KT1I4.H20 

(NH4)8T1C16  (NH4)TlBr4.5H20 

(NH4)TlBr4.2H20 

(NH4)TlBr4 

(NH4)T1I4 

Several  points  of  interest,  already  noticed  in  connection 
with  double  salts  prepared  in  this  laboratory,  are  well  illus- 
trated by  the  series  of  new  compounds  to  be  described.  With 
caesium,  a  more  complete  series  of  salts  was  prepared  than 
with  the  other  alkali  metals ;  and  there  is  also  an  increase  in 
ease  of  formation  and  in  number  of  salts,  from  the  iodides  to 
the  chlorides.  The  salts,  formed  from  the  alkali  metal  with 
the  lower  atomic  weight  are  generally  more  soluble  in  water, 
form  in  larger  crystals  and  with  more  water  of  crystallization 
than  those  with  higher  atomic  weight. 

Preparation.  —  The  double  salts  were  prepared  in  each  case 
by  mixing  solutions  of  the  thallic  halide  with  the  alkali  halide 
in  widely  varying  proportions,  evaporating  and  cooling  to 
crystallization.  With  the  bromides  and  iodides  the  conditions 
for  obtaining  the  double  salts  were  improved  by  the  presence 
of  a  little  free  bromine  and  iodine. 

The  crystals,  soon  after  forming,  were  removed  from  the 
solutions,  quickly  pressed  between  filter  papers  to  remove  the 
mother-liquor,  and,  with  the  exception  of  the  sodium  and 
lithium  salts,  allowed  to  stand  exposed  to  the  air  for  some 
time.  The  latter,  on  account  of  their  instability,  were  placed 
in  tightly  stoppered  weighing-tubes  as  soon  as  they  were  free 
from  the  mother-liquor. 

Method  of  Analysis.  —  In  determining  thallium,  the  salt  was 
dissolved  in  warm  water  and  a  slight  excess  of  ammonium 
sulphide  added  to  precipitate  the  thallium  as  thallous  sulphide. 
This  was  filtered  and  washed  with  water  containing  a  little 
ammonium  sulphide.  The  precipitate  was  then  dissolved  in 
hot  dilute  nitric  acid,  the  solution  evaporated  with  sulphuric 
acid  in  a  platinum  crucible,  and  then  heated  to  constant  weight 


372        DOUBLE  HALIDES  OF  CAESIUM,  RUBIDIUM, 

within  a  porcelain  crucible  over  a  small  flame.  The  nitrate 
from  the  thallous  sulphide  precipitation  was  evaporated  with 
sulphuric  acid,  the  ammonium  salts  driven  off,  and  the  residual 
alkali  sulphate  ignited  in  a  stream  of  air  containing  ammonia. 
The  halogens  were  determined  as  silver  salts  in  separate  por- 
tions, with  the  precaution  of  adding  sulphurous  acid  in  the 
case  of  the  iodides  to  prevent  loss  of  iodine  in  dissolving,  and 
it  was  found  to  be  necessary  in  all  cases  to  use  a  large  excess 
of  nitric  acid  in  order  to  obtain  the  silver  halide  in  a  pure  con- 
dition. Water  was  determined  by  igniting  in  a  combustion 
tube,  behind  a  layer  of  dry  sodium  carbonate,  in  a  stream  of 
dry  air  and  collecting  it  in  a  weighed  calcium  chloride  tube. 

3:1  Ccesium  and  Rubidium  Thallic  Chlorides,  CssTlCl6. 
H20  and  RbsTlCl6.HzO.  —  The  ceesium  salt  is  obtained,  as  a 
white  precipitate,  when  0.25  g.  of  thallic  chloride  is  added  to 
a  solution  of  50  g.  of  caesium  chloride.  The  precipitate  dis- 
solves somewhat  slowly  upon  heating  the  solution,  and  crystal- 
lizes out  on  cooling.  The  range  of  conditions  is  very  narrow 
as  3  g.  of  thallic  chloride  to  50  g.  of  caesium  chloride  give  the 
salt,  Cs3TlCl9.  The  salt  is  soluble  in  hot  water,  but  Cs3Tl2Cl9 
crystallizes  from  the  solution. 

The  rubidium  salt  has  a  much  wider  range  of  formation.  It 
is  obtained  when  1.5  to  25  g.  of  thallic  chloride  are  added  to  a 
solution  of  40  g.  of  rubidium  chloride.  It  is  very  soluble  in 
cold  water,  but  gives  another  salt,  Rb2TlCl6.H2O  upon  crystal- 
lization. Both  salts  are  white,  as  are  all  the  chlorides  with 
one  exception.  Two  separate  crops  of  each  were  analyzed  with 
the  following  results  :  Found. 

.  Calculated  for 


A.  B. 

Caesium      .     .     .    48.44  48.05      48.33  47.84 

Thallium    .     .     .     24.21  24.45      24.37  24.46 

Chlorine     .     .    .    25.37  25.53       .  .  .  25.54 

Water    ....      2.74  1.97       .  .  .  2.16 

Found.  Calculated  for 

A.  B.  Rb8TlCl6.H80. 

Rubidium    ......  36.54  37.09 

Thallium     .    .     .     29.02  29.65  29.50 

Chlorine.    .     .     .    30.99  31.17  30.81 

Water     ....      2.51  1.72  2.60 


SODIUM,  AND  LITHIUM  WITH  THALLIUM.    373 

The  caesium  salt  was  obtained  in  hair-like  crystals,  too  small 
for  measurement.  The  rubidium  salt  crystallized  in  thin  plates 
having  a  rhombic  outline.  Under  the  microscope  these  showed 
an  extinction  parallel  to  the  diagonals  and  in  convergent  light 
a  bisectrix  at  one  side  of  the  field,  with  the  plane  of  the  optic 
axes  at  right  angles  to  the  longer  diagonal,  indicating  mono- 
clinic  symmetry. 

2  :  1  Ccesium  and  Rubidium  Thallic  Chlorides,  Cs^TlCl^ 
Cs2TWlB.ff20,  and  EbzTWl5.ff20.  —  The  anhydrous  caesium 
salt  is  formed  when  5  to  8  g.  of  thallic  chloride  are  added  to  a 
somewhat  concentrated  solution  of  100  g.  of  caesium  chloride, 
and  the  hydrous  salt,  when  8  to  15  g.  of  thallic  chloride  are 
added  to  a  more  dilute  solution  of  100  g.  of  caesium  chloride. 
The  rubidium  salt  was  observed  when  1.25  to  18  g.  of  rubidium 
chloride  were  added  to  a  rather  concentrated  solution  of  30  g. 
of  thallic  chloride.  The  two  hydrous  salts  are  white  and  the 
anhydrous  compound  is  pale  green.  The  caesium  salts  are 
readily  soluble  in  hot  water,  but  the  salt  Cs8Tl2Cl9  crystallizes 
from  the  solution.  The  rubidium  salt  recrystallizes  unchanged 
from  water.  The  following  analyses  were  made  upon  separate 
crops : 


Found. 

Calculated  for 


A.  B.  C82T1C16. 

Osmm 40.46  40.17  41.07 

Thallium  .     .     .     31.11  31.82  31.62  31.52 

Chlorine    .     .     .     27.19  27.30  27.20  27.41 

Water 81  ...  .81 

The  small  amount  of  water  found  in  the  above  analyses, 
equivalent  to  about  one-fourth  of  a  molecule,  was  probably 
held  mechanically  by  the  crystals. 

Found. 
., • v  Calculated  for 


A.  B.  C.  C8,T1C15.H,0. 
I.                  II. 

Osium     .     .    40.03      39.84  40.30  39.85  39.97 

Thallium  .    .     30.75      30.71  31.11  30.98  30.65 

Chlorine  .    .    26.85       .  .  .  26.56  26.93  26.67 

Water .              .  ,  .  2.88  2.37  2.71 


374       DOUBLE  HALIDES  OF  CAESIUM,  RUBIDIUM, 


Found. 
A.                      B. 

29.09        28.97 

Calculated  for 
Rb2TlCl5.H2O. 

29.97 

35.94 

35.74 

35.76 

30.74 

30.97 

31.11 

3.34 

•  •  • 

3.16 

Rubidium 
Thallium 
Chlorine 
Water 


The  crystals  of  Cs2TlCl6  were  in  needles  too  small  for 
measurement. 


The  crystallization  of 
Cs2TlCl5.H2O  and  Rb2 
T1C16.H2O  is  orthorhom- 
bic.  The  salts  are 
similar  in  habit  and  are 
developed  as  in  Figs.  1 
and  2.  The  forms  ob- 
served are  as  follows : 


a,  100 
m  110 


e,  102 


The  crystals  of  the  csesium  salt  were  only  about  .4  to  .6  mm. 
in  length,  but  the  faces  were  smooth  and  gave  good  reflections 
on  the  goniometer.  The  axial  ratio  is, 

a  :  I  :  b  =  0.6762  :  1  :  0.6954. 


JA  4  Oil  A  OT1 
m  Am,  110  A  1TO 
m  A  a,  110  A  100 

a  A  e,  100  A  102 
m  A  d,  110  A  Oil 
<*A  e,  Oil  A  102 

e  A  e,  102  A  T02 


Crystals  of  the  rubidium  salt  were  obtained  from  about  1.5 
to  4  mm.  in  length.    The  axial  ratio  is, 

a  -.I-.  c  =  0.6792:  1:0.7002. 


Measured. 

Calculated 

*70° 

... 

*68° 

22' 

... 

34° 

3'  30" 

34°  11' 

62° 

51' 

62°  44' 

71°  14'; 

71°  16' 

71°  12' 

43° 

9' 

43°  16' 

54° 

6' 

54°  32' 

SODIUM,   AND  LITHIUM   WITH  THALLIUM.        375 

Measured.  Calculated. 


AOT1  *69°  36' 

m  A  m,  110  A  1TO  *68°    7£'  ... 

m  A  a,  110  A  100  34°  4';  34°  9';  34°  5'        34°    4' 

a  A    e,  100  A  102  62°  52£'  62°  49' 

m  A  d,  110  A  Oil  71°  26>  ;  71°  23'  71°  21' 

d*    e,  Oil  A  102  43°  19'  43°    4£ 

e  A   «,  102  A  T02  54°  15'  54°  22' 


3  :  2  Ccesium  Thallic  Chloride,  CssTl2Cl9.  —  ThQ  conditions 
under  which  this  salt  can  be  made  are  very  wide  ;  .5  to  29  g. 
of  caesium  chloride  form  a  heavy  white  precipitate  when  added 
to  a  solution  of  40  g.  of  thallic  chloride.  This  dissolves  read- 
ily in  the  solution  upon  heating  and  crystallizes  in  slender 
hexagonal  prisms  terminated  by  the  pyramid.  When  the  ratio 
of  the  csesium  chloride  to  the  thallic  chloride  is  30  g.  to  50  g., 
a  salt  is  obtained  which  crystallizes  in  hexagonal  plates. 
Analyses  of  the  plates  do  not  agree  very  closely  with  theory, 
but  it  is  evident  that  they  are  the  same  as  the  prismatic  salt 
with  another  crystalline  habit.  The  high  percentage  of 
csesium  and  the  corresponding  low  percentage  of  thallium  is 
probably  due  to  the  slight  inclusions  held  by  the  crystals, 
which  could  be  seen  with  the  microscope.  This  salt  is  white, 
permanent  in  the  air,  and  recrystallizes  unchanged  from  water. 
The  analyses  given  below  are  of  separate  crops  made  under 
very  different  conditions. 

Caesium.  Thallium.  Chlorine.  Water. 

A    ....     34.93  ...  ...  .65 

B    .     .    .    .     35.09        35.64-35.51        28.09-27.99 

C    .......  ...  28.06;  .95 

D    .......  35.63 

E    .     .     .     .    35.03  35.69  28.06 

F  (Plates)     .    36.64  33.85  28.15 

G  (Plates)     .    36.18  34.46  28.18  .61 


The   water  found  in  these  analyses  was    probably  held 
mechanically  by  the  crystals. 


376       DOUBLE  HALIDES  OF  CESIUM,  RUBIDIUM, 

The  prismatic  variety  of  this  salt  showed  only  the  forms  of 
the  prism,  1010,  and  pyramid,  1011. 

Axis  c  =  0.82566 ;  0001  A  10T1  =  43°  37'  50" 

Measured.  Calculated. 

p^p,  lOIlAOlTl       *40°  21' 

m*p,  10TO  A  10T1        46°  21 J' ;  46°  22'        46°  22' 

Sections  parallel  to  the  basal  plane  show  in  convergent 
polarized  light  the  normal  uniaxial  interference  figure,  with 
weak  negative  double  refraction.  The  crystals  served  very 
well  as  60°  prisms  for  the  determination  of  the  indices  of 
refraction  with  the  following  results : 

Red,  Li.  Yellow,  Na.  Green,  Tl. 

<o=        1.772  1.784  1.792 

€=        1.762  1.774  1.786 

3:1  Rubidium  Thallic  Bromide,  1$.  275r6.5, 0.  —  Tffis 
salt  was  formed,  when  1.5  to  24  g.  of  thallic  bromide  were 
added  to  a  very  concentrated  solution  of  50  g.  of  rubidium 
bromide.  It  crystallizes  in  beautiful  golden  yellow  crystals, 
which  are  very  soluble  in  water,  giving  the  1  :  1  salt  on  re- 
crystallizing.  Careful  efforts  were  made  to  obtain  a  2  :  1  and 
3  :  2  rubidium  thallic  bromide,  but  without  success.  Several 
separate  products,  made  under  very  different  conditions,  were 
analyzed  with  the  results  which  follow: 

Bromine.  Water. 

49.29          2.49 
49.66 

49.42 
50.28 

50.49 

50.08          1.88 

The  somewhat  high  percentage  of  rubidium  and  the  low 
percentage  of  thallium  found  in  the  first  four  analyses  is  prob- 


A   .... 

Rubidium. 

.    28.57 

Thallium. 

B    .         .     . 

2039 

C    .    . 

28.18 

2059 

D   .     .     .     . 

2803 

2016 

E    .     .    .     . 

2770 

2033 

F    .     .    . 

2064 

G   .    .     .     . 

.    26.56 

21.17 

Calculated  for 
Kb8TlBr6.H20 

1   26.76 

21.28 

SODIUM,  AND  LITHIUM    WITH  THALLIUM.        377 

ably  due  to   the    large    excess    of    rubidium  3 

bromide  in  the  concentrated  solutions  from 
which  the  crystals  were  obtained.  As  more 
thallic  bromide  was  added,  better  crystals  were 
obtained  in  more  dilute  solutions,  which  give 
percentages  agreeing  very  well  with  the  cal- 
culated. 

The  crystallization  of  this  salt  is  tetragonal. 
Doubly  terminated  crystals  were  obtained  up 
to  a  length  of  6  mm. 

The  forms  observed  are : 

a,  100  m,  110  ft  111 

c,  001  e,  101 

The  habit  is  shown  in  Fig.  3. 

Axis  b  =  0.80728 ;  001  A  101  =  38°  54'  45" 

Measured.  Calculated. 


e  A  e,  T01  A  101  *77° 

a  A  e,100  A  101  51°    6';  51°    2';  51°    3£'  51°    5^' 

a  A  p,  100  A  111  57°  52' ;  57°  54' ;  57°  53'  57°  52' 

e  Aft  101  A  111  32°    5' ;  32°  12'  32°    8' 

c  Aft  001  A  111  48°  51' ;  48°  55'  48°  46' 

m  Aft  110  A  111  41°    7' ;  41°    4'  41°  13' 

The  crystals  show  a  weak  negative  double  refraction. 

3  :  2  Ccesium  Thallic  Bromide,  Cs8TlzBr9.  —  This  salt  was 
observed,  as  yellowish  red  crystals,  when  1  to  15  g.  of  thallic 
bromide  were  added  to  a  solution  of  50  g.  of  caesium  bromide. 
It  was  always  obtained  in  small  striated  crystals,  which  were 
not  adapted  for  measurement.  It  is  permanent  in  the  air  and 
recrystallizes  unchanged  from  water.  Analyses  of  separate 
products  gave  the  following  results : 

Fo"nd-  Calculated  for 


Caesium  . 

A. 

B. 

26.52 

c. 
26.14 

D. 

Thallium 
Bromine 

.    .    27.36 
.    .    47.24 

27.21 
47.14 

27.28 
47.08 

47.27 

26.13 
26.72 
47.15 


378       DOUBLE   HALIDES  OF  CJESIUM,  RUBIDIUM, 

1  :  1  Ccesium  and  Rubidium  Thallic  Bromides,  CsTlBr± 
and  RbTlBr^.HzO.  —  These  two  salts  are  of  nearly  the  same 
color,  pale  yellow.  The  rubidium  compound,  which  retains  its 
lustre  and  color  much  better  than  the  other,  recrystallizes 
unchanged  from  water,  while  the  caesium  salt  gives  Cs3Tl2Br9, 
when  its  solution  is  evaporated  to  crystallization.  The  caesium 
salt  was  observed  when  2  to  10  g.  of  caesium  bromide  were 
added  to  40  g.  thallic  bromide,  and  the  rubidium  salt  when  3  to 
24  g.  of  rubidium  bromide  were  added  to  40  g.  thallic  bromide. 
Analyses  of  several  different  crops  gave  the  following  results  : 

Found-  Calculated  for 

CsTlBr4. 

20.25 
31.05 
48.70 

Calculated  for 
RbTlBr4.H2O. 

13.63 
32.51 

50.99 

2.87 

The  crystallization  of  these  two  salts  is  isometric,  the  cube 
being  the  only  form  observed. 

1  :  1  Ccesium  and  Rubidium  Thallic  Iodides,  CsTlI±  and 
Rb  TlIi.Hz  0.  —  Both  of  these  salts  were  prepared  from  solu- 
tions containing  a  large  excess  of  thallic  iodide  and  also  from 
solutions  containing  a  large  excess  of  the  alkali  iodide,  so  that 
no  other  type  of  double  iodides  with  these  two  metals  could  be 
obtained.  As  the  thallic  iodide  was  very  difficultly  soluble  in 
water,  alcoholic  solutions  were  used  where  the  thallic  iodide 
was  in  excess.  The  salts  are  ruby  red,  with  a  brilliant  lustre, 
which  is  slowly  lost  in  the  air.  Both  are  decomposed  by  water. 
The  analytical  results  obtained  from  several  different  crops  are 
given  below: 

"*  Calculated  for 


CsBsium 

A. 

.    .    19.14 

B.                C. 

D. 

20.44 

Thallium 
Bromine 

.     .    32.36      31 
47.76 

.79      32.04 
.  .       48.39 

Found. 

48.88 

Kubidium 
Thallium  . 
Bromine  . 
Water  . 

A. 

.     .    .     13.77 
.    .     .    32.18 
.    .     .    50.06 
3.80 

B. 

13.41 

*     •     • 

c. 
13.91 

50^30 

A  B. 

Caesium    ....     16.57  16.38  .  .  .  15.74 

Thallium  ....     24.09  24.04  .  .  .  24.14 

....  59.48  59.67  60.12 


SODIUM,  AND  LITHIUM   WITH  THALLIUM.        379 


Found. 


Kubidium 
Thallium 
Iodine  . 
Water  . 


10.34 
24.98 

60.38-60.32 
4.50 


B. 

9.78 
25.23 
60.79 


Calculated  for 
RbTU4.2H,O. 

10.26 

24.47 

60.94 

4.32 


These  salts  crystallize  in  the  isometric  system,  the  habit  being 
usually  the  cube  truncated  by  the  octahedron. 

3  :  1  Sodium  and  Lithium  Thallic  Chlorides,  NasTlCl6.W 
Hz  0  and  Liz  Tl  OlQ.8ff2  0.  —  Only  one  type  of  double  salts  could 
be  obtained  with  these  metals,  and  it  does  not  seem  possible 
that  others  exist,  for  the  ground  was  covered  very  carefully 
and  systematically.  On  account  of  the  extreme  solubility  of 
these  salts,  especially  that  of  the  lithium  compound,  the 
solutions  had  to  be  kept  very  concentrated,  in  a  more  or  less 
syrupy  condition,  which  accounts  for  the  high  alkali  metal  and 
low  thallium  found.  These  salts  are  transparent  and  colorless 
when  first  taken  from  the  mother-liquor,  but,  upon  exposure 
to  the  air,  the  sodium  salt  becomes  opaque  and  the  lithium 
compound  deliquesces.  Analyses  of  different  products  gave 
the  following  results : 


Found. 


Sodium 11.13 

Thallium    ....  27.79 

Chlorine     ....  31.23 
Water 


Lithium 
Thallium 
Chlorine . 
Water 


B. 

10.48 
28.39 
30.45 
29.75 


Calculated  for 


Found. 

1 

A. 

.      3.71 
.    34.51 
.    36.09 
25.14* 

B. 

3.79 

c. 
3.73 

D. 

3.78 

36.01 

36.40 

36.31 

9.83 
29.06 
30.34 
30.77 

Calculated  for 
Li8TlCl«.8H,0. 

3.61 
35.06 
36.59 
24.74 


On  account  of  the  instability  of  the  sodium  and  lithium 
salts  no  crystallographic  determinations  were  made. 

Repeated  attempts  to  prepare  lithium  and  sodium  thallic 


By  difference. 


380  DOUBLE  HALIDES   WITH  THALLIUM. 

bromides  were  entirely  without  success,  hence  no  attempt  was 
made  to  prepare  the  iodides. 

The  author  wishes  to  express  his  indebtedness  to  Prof.  H.  L. 
Wells  for  valuable  advice  in  connection  with  the  chemical  part 
of  this  work,  and  to  Prof.  S.  L.  Penfield  for  suggestions  con- 
cerning the  crystallography. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
December,  1894. 


ON  THE  DOUBLE  SALTS  OF  CESIUM  CHLORIDE 
WITH  CHROMIUM  TRICHLORIDE  AND  WITH 
URANYL  CHLORIDE.* 

BY  H.  L.  WELLS  AND  B.  B.  BOLTWOOD. 

NEUMANN!  has  made  an  extensive  investigation  of  the 
double  salts  formed  with  chromium  trichloride  and  the  chlo- 
rides of  several  other  metals,  not,  however,  including  caesium. 
He  obtained  a  violet  double  salt  in  each  case  with  ammonium, 
potassium,  rubidium,  beryllium,  and  magnesium,  corresponding 
to  the  general  f ormula,  2M'C1.  CrCl8.H2O,  while  with  lithium, 
sodium,  calcium,  strontium,  barium,  zinc,  and  cadmium  he  was 
unable  to  prepare  any  double  compounds.  The  double 
fluorides,  2NH4F.CrF8.H2O,  and  2KF.CrF8.H2O,  which  are 
analogous  to  Neumann's  salts,  have  been  mentioned  by  Wag- 
ner, J  who  also  prepared  the  compounds  4NaF.2CrF8.H2O 
and  3NH4F.CrF3.  The  existence  of  the  latter  salt  has  been 
confirmed  by  Petersen.  § 

Since  Neumann  had  not  prepared  any  caesium-chromium 
chloride,  and  because,  from  the  well-known  comparative  insolu- 
bility of  caesium  double  salts,  it  seemed  possible  that  a  greater 
variety  of  compounds  would  be  obtained  with  this  than  with 
other  metals,  we  have  undertaken  an  investigation  in  this 
direction.  As  the  result  of  a  systematic  search,  however,  we 
have  added  only  a  variation  in  water  of  crystallization  to 
Neumann's  general  formula. 

Two  salts  have  been  obtained.  One  of  these,  2CsCl.CrCls. 
H2O,  is  violet  in  color,  corresponding  exactly  to  Neumann's 
compounds,  while  the  other,  2CsCl.CrCl8. 4H2O,  is  green. 
The  violet  salt  was  prepared  by  saturating  warm  aqueous 
solutions  containing  various  proportions  of  the  two  simple 
chlorides  with  gaseous  hydrochloric  acid.  The  green  salt  was 

*  Amer.  Jour.  Sci.,  1, 1895.  t  Liebig's  Annalen,  ccxliv,  329. 

|  Berichte,  xix,  896.  §  J.  prakt.  Chem.,  II,  Ix,  52. 


382  DOUBLE  SALTS  OF  CESIUM  CHLORIDE 

obtained  from  cold  solutions  by  the  use  of  hydrochloric  acid, 
and  without  its  use  by  evaporation  over  sulphuric  acid. 

The  salt  2CsCl.CrCls.H2O  forms  aggregates  of  very  minute 
crystals  of  a  magnificent  red-violet  color.  It  is  stable  in  the 
air  and  does  not  lose  its  water  at  160°.  It  is  very  slowly 
soluble  in  cold  water,  forming  a  green  solution  from  which 
the  green  salt  is  deposited  upon  evaporation  at  ordinary  temper- 
atures. The  four  crops  analyzed  were  prepared  with  amounts 
of  caesium  chloride  and  chromic  chloride  varying  from  15  g.  of 
the  first  and  50  g.  of  the  second  to  50  g.  of  the  first  and  10  g. 
of  the  second.  Gaseous  hydrochloric  acid  caused  a  deposition 
of  the  salt  from  warm  solutions.  The  products,  after  careful 
drying  with  paper  and  over  sulphuric  acid,  gave  the  following 
results  upon  analysis  : 

F<Td-  Calculated  for 

2CsCl.CrCls.H20. 


A. 

B. 

c. 

D. 

Caesium    .    . 

50.31 

49.72 

49.64 

.    .    . 

Chromium 

10.44 

10.53 

10.68 

10.70 

Chlorine    .     . 

34.65 

34.77 

34.37 

... 

Water  .     .     . 

4.11 

5.12 

99.51 

10014 

The  salt  2CsCl.CrCl3.4H2O  is  deposited  from  cold  concen- 
trated solutions  in  the  form  of  green,  apparently  monoclinic 
crystals.  It  is  somewhat  deliquescent,  very  soluble  in  water, 
and  loses  no  water  in  the  desiccator  over  sulphuric  acid.  At 
110°  it  readily  loses  three  molecules  of  water  and  is  converted 
into  the  violet  salt.  Three  crops  analyzed  were  prepared  as 
follows :  Crop  A,  by  evaporating  a  solution  of  50  g.  caesium 
chloride  and  25  g.  of  chromic  chloride  ;  Crop  B,  by  dissolving 
the  violet  salt  in  water  and  evaporating  over  sulphuric  acid ; 
Crop  C,  by  cooling  a  concentrated  solution  of  50  g.  of  each 
chloride  with  the  aid  of  ice  and  saturating  it  with  hydrochloric 
acid.  The  results  were  as  follows : 


Found-  Calculated  for 


A. 

B. 

c. 

2CsCl.CrCls.< 

Caesium      .    .     . 

.    46.40 

46.13 

46.73 

46.86 

Chromium      .     . 

.      9.80 

9.53 

10.79 

9.19 

Chlorine     .     .     . 

.     31.30 

31.14 

. 

31.27 

Water   .... 

.      ... 

... 

•  •  • 

12.68 

WITH  CHROMIUM  TRICHLORIDE,  ETC.  383 

A  determination  was  also  made  of  the  water  lost  at  110° : 

w^r,^  Calculated  for 

3H20  in  2CsCl.CrCl3.4H,0. 

Water 9.90  9.51 

The  variation  in  color  of  the  two  salts  that  have  just  been 
described  is  interesting  in  connection  with  the  violet  and 
green  modifications  of  chromic  salts  in  general,  which  have 
furnished  the  ground  for  much  investigation  and  discussion. 
In  the  case  under  consideration  the  transformation  from  one 
color  to  the  other  is  accomplished  by  the  addition  or  subtrac- 
tion of  water.  It  seems  highly  probable,  however,  that  the 
change  in  water  is  accompanied  by  a  fundamental  change  in 
the  molecular  structure,  because  the  violet  salt,  containing 
the  smaller  amount  of  water,  is  very  much  more  slowly 
soluble  in  water  than  the  green  salt,  forming  like  the  latter 
a  green  solution.  We  have  found  that  the  whole  of  the  chlo- 
rine in  the  cold  green  solutions  of  these  caesium  salts  is  not 
precipitated  as  silver  chloride,  thus  showing  that  they  agree 
in  this  respect  with  other  green  solutions  of  chromic  chloride. 

It  is  a  curious  circumstance  that  the  green  chromic  sul- 
phate has  been  considered*  to  contain  less  water  than  the 
violet  modification,  while  with  our  caesium  salts  exactly  the 
reverse  is  true,  the  green  salt  containing  the  larger  amount  of 
water.  It  is  also  remarkable  that,  while  violet  chromic  solu- 
tions are  turned  green  by  heat,  our  violet  salt,  nevertheless, 
is  produced  hi  hot  solutions  and  the  green  salt  in  cold  ones. 
The  theory  advanced  by  Kriiger  and  maintained  by  Van  Cleeff  f 
that  the  green  color  of  chromic  sulphate  solutions  is  due  to  the 
formation  of  a  basic  salt  and  free  acid  or  an  acid  salt,  seems 
hardly  applicable  to  the  green  caesium  salts,  since  it  crystal- 
lizes from  solutions  saturated  with  hydrochloric  acid  in  which 
a  basic  salt  would  seem  to  be  an  impossibility.  In  view  of 
these  apparently  conflicting  facts,  it  seems  necessary  to 
draw  the  conclusion  that  the  differences  in  color  exhibited 
by  chromic  compounds  and  their  solutions  are  due  to  more 

*  Vide  Van  Cleeff,  J.  prakt.  Chem.,  II,  xxiii,  68.  f  Loc.  cit. 


384      DOUBLE  SALTS  OF  CESIUM  CHLORIDE,  ETC. 

than  one  cause,  probably  to  the  formation  of  basic  salts  in 
certain  cases,  and  also,  in  other  instances,  to  a  change  in  water 
of  crystallization  which  is  evidently  accompanied  by  a  molecu- 
lar transformation. 

Uranyl  Chloride  and  Ccesium  Chloride.  —  A  careful  series 
of  experiments  with  caesium  chloride  and  uranyl  chloride 
has  resulted  in  the  discovery  of  but  a  single  salt.  This 
compound,  2CsCl.UO2Cl2,  corresponds,  except  that  it  con- 
tains no  water,  to  the  previously  described  salts,  2KC1. 
U02C12.2H20,  2KBr.UO2Br2.2H2O,  2NH4C1.UO2C12.2H2O,  and 
2NH4Br.UO2Br2.2H2O,  but  some  fluorides  of  other  types 
have  been  described. 

The  compound  under  consideration  forms  apparently  ortho- 
rhombic,  yellow  crystals  which  are  usually  small  and  blade-like 
in  shape.  The  products  used  for  analysis  were  made  under 
the  following  conditions :  Crop  A,  by  making  a  concentrated 
aqueous  solution  of  10  g.  of  caesium  chloride  and  50  g.  of 
uranyl  chloride,  then  running  in  gaseous  hydrochloric  acid 
until  crystals  began  to  form  and  cooling;  Crop  B,  by  the 
same  method  as  above,  using  50  g.  of  caesium  chloride  and 
10 g.  of  uranyl  chloride;  Crops  C  and  D,  by  spontaneous 
evaporation  of  solutions  containing  50  g.  of  caesium  chloride 
and  15  g.  of  uranyl  chloride ;  and  E,  by  the  evaporation  of 
a  solution  of  15  g.  of  caesium  chloride  and  50  g.  of  uranyl 
chloride.  The  results  were  as  follows: 


Fo"nd>  Calculated  for 


AT^  B.  C.  ~~D~        ~1T  2C8C1.U02C12. 

Cs    .     .    39.43      39.63      40.07       39.15 

U02      .    40.37      41.14      40.96      41.85      43.39  39.95 

Cl    .     .    20.63      21.17      20.85      20.84      20.59  20.90 

The  caesium  chloride  used  in  this  investigation  was  from 
a  liberal  supply  of  caesium  and  rubidium  salts  presented  to 
this  laboratory,  for  the  encouragement  of  scientific  research, 
by  Herr  E.  Merck  of  Darmstadt,  Germany,  and  we  wish  to 
express  our  sincere  thanks  to  him  for  his  generosity. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
June,  1895. 


ON  THE  AMMONIUM-CUPROUS  DOUBLE 
HALOGEN   SALTS.* 

BY  H.  L.  WELLS  AND  E.  B.  HURLBUBT. 

THE  existence  of  ammonium-cuprous  double  halides  has  long 
been  known,  but  since  no  complete  investigation  of  these 
compounds  had  been  made,  a  careful  study  of  them  has 
been  undertaken. 

Mitscherlich  f  prepared  the  potassium  salt  4KCl.Cu2Cl2, 
and  mentioned  the  corresponding  ammonium  salt.  This 
salt,  4NH4Cl.Cu2012,  has  been  obtained  in  the  present 
investigation. 

Deherain  J  described  three  double  chlorides,  4NH4Cl.Cu2Cl2. 
H2O,  2NH4Cl.Cu2Cl2,  and  NH.Cl.C^CL,.  The  first  of  these 
salts,  if  the  molecule  of  water  is  omitted,  corresponds  to  the 
compound  mentioned  by  Mitscherlich  which  we  have  obtained, 
and  we  are  convinced  that  Deherain's  formula  for  it  is  wrong. 
The  second  salt,  2NH4Cl.Cu2Cl2,  has  not  been  obtained  by  us, 
but  since  it  corresponds  in  type  to  a  bromide  and  an  iodide 
which  are  easily  prepared,  its  existence  seems  possible.  The 
third  salt  of  Deherain,  NH4Cl.Cu2Cl2,  probably  does  not  ex- 
ist, for  we  have  failed  to  obtain  it,  as  has  Ritthausen  also. 
Ritthausen,  §  while  not  being  able  to  prepare  NH4Cl.Cu2Cl2, 
obtained  the  compound  4NH4C1.3Cu2Cl2,  and  we  have  con- 
firmed this  result.  The  compositions  required  for  the  two 
formulae  do  not  differ  widely,  so  that  it  is  probable  that 
Deherain  analyzed  the  salt  4NH4C1.3Cu2Cl2  and  gave  it  an 
incorrect  formula. 

As  far  as  we  know,  no  double  bromides  have  been  previously 
described.  Saglier  ||  has  described  an  ammonium-cuprous 

*  Amer.  Jour.  Sci.,  1, 1895.  t  Ann.  Chim.  Phys.,  Ixxiii,  384. 

J  Compt.  rend.,  Iv,  808.  §  J.  prakt.  Chem.,  lix,  369. 

II  Compt.  rend.,  civ,  1440. 

25 


386  ON  THE  AMMONIUM-CUPROUS 

iodide,  to  which  the  formula  2NHJ.Cu2I2.H2O  is  given. 
The  single  double  iodide  which  we  have  obtained  corresponds 
to  Saglier's  description  and  to  his  formula,  except  that  we 
have  found  it  to  be  undoubtedly  anhydrous. 

In  the  present  investigation  a  great  number  of  experiments 
have  been  made,  with  gradually  varying  proportions  of  the 
constituent  salts  in  each  case,  in  order  to  obtain  as  many  com- 
pounds as  possible. 

The  Chlorides,  ^NH^Cl.OuzClz  and  ^NH^Cl.3 CuzClz.  - 
These  compounds  were  prepared  by  making  hot  hydrochloric 
acid  solutions  of  mixtures  of  the  simple  salts,  usually  in  the 
presence  of  copper  wire,  and  cooling  to  crystallization.  The 
first  salt  mentioned  above  is  very  readily  oxidized  by  exposure 
to  air ;  hence  it  has  been  found  advisable  in  making  it  to  use  a 
flask  and  to  protect  the  solution  from  air  by  means  of  a  stream 
of  carbonic  acid. 

The  compound  4NH4Cl.Cu2Cl2  requires  the  presence  of  a 
comparatively  large  amount  of  ammonium  chloride  for  its  for- 
mation, and  crystallizes  in  colorless  prisms  which  rapidly  change 
in  color  through  brown  to  green  upon  exposure  to  the  air. 
Crystals  20  mm.  in  length  and  5  mm.  in  thickness  were  observed. 

The  following  analyses  of  two  separate  crops  were  made : 

•n>nnn  j  Calculated  for 

Found.  4NH.Cl.Cu.Cl* 

Ammonium   .....     17.91  18.12  17.48 

Copper 29.69  29.28  30.79 

Chlorine 50.66  50.37  51.73 

98.26  97.77  100.00 

It  was  necessary  to  dry  the  samples  for  analysis  very  rapidly 
on  account  of  their  instability,  and  some  water  was  unavoidably 
left  in  them,  causing  the  low  summations.  The  amount  of 
water  corresponding  to  one  molecule  (Deherain's  formula)  is 
4.19  per  cent. 

The  other  chloride,  4NH4C1.3Cu2Cl2,  is  produced  when 
the  simple  salts  are  mixed  in  the  required  proportion  in  hydro- 
chloric acid  solution,  and  also  under  considerable  variations  from 
these  proportions.  It  forms  brilliant,  colorless  dodecahedra 


DOUBLE  HALOGEN  SALTS  387 

which  are  moderately  stable  in  the  air  at  ordinary  temperatures, 
but  gradually  turn  green  on  exposure. 

The  following  analyses  of  three  separate  crops  were  made : 

F(Td-  Calculated  for 


Ammonium  . 

i. 
.       9.39 

n. 
9.73 

ILL 

9.73 

8.92 

Copper  .  . 
Chlorine  .  . 

.    47.19 
.     42.81 

46.73 
43.11 

46.79 
43.13 

47.15 
43.93 

99.39 

99.57 

9065 

100.00 

The  calculated  amounts  of  ammonium,  copper,  and  chlorine 
for  Deherain's  formula,  NH4Cl.Cu2Cl2,  are  7.15, 50.50,  and  42.35 
respectively,  and  it  does  not  seem  possible  that  this  formula 
represents  the  true  composition  of  the  salt,  because  the  samples 
analyzed  were  well  crystallized  and  evidently  very  pure. 

The  Bromides,  4NH±Br.  Cu2Brz  and  2NH^Br.CuzBrz.HzO. 
-  By  the  use  of  ammonium  bromide,  cuprous  bromide,  hydro- 
bromic  acid,  and  copper  wire,  these  compounds  were  produced 
similarly  to  the  chlorides,  but  since  these  salts  oxidize  much 
less  readily  than  the  chlorides,  no  protection  by  means  of 
carbon  dioxide  was  necessary  in  any  case. 

The  first  salt,  4NH4Br.Cu2Br2,  is  formed  in  the  presence 
of  an  excess  of  ammonium  bromide,  and  resembles  the  corre- 
sponding chloride  in  form,  occurring  in  long,  colorless  prisms 
which  turn  green  after  long  exposure  to  the  air.  Analyses  of 
two  separate  crops  gave : 

Found.  Calculated  for 

I.  II.  4NH4Br.Cu3Br,. 

Ammonium 10.24  10.24  10.61 

Copper 18.81  18.47  18.68 

Bromine 70.93  70.60  70.71 

99.98  99.31  100.00 

The  other  bromide,  2NH4Br.Cu2Br2.H2O,  is  formed  in 
the  presence  of  a  relatively  greater  amount  of  cuprous  bromide. 
It  forms  brilliant,  colorless  rhombohedra,  sometimes  15  mm. 
long  and  9  mm.  wide,  and  it  is  more  stable  in  the  air  than  the 
first  bromide.  Analyses  of  two  separate  crops  gave  : 


388  ON  THE  AMMONIUM-CUPROUS 

Pound.  Calculated  for 

I.  II.  2NH4Br.Cu2Br,.H20. 

Ammonium 6.88  6.90  7.19 

Copper 25.61  25.20  25.32 

Bromine 63.76  64.08  63.90 

Water  (difference)  .     .     .  3.75  3.82  3.59 

The  Iodide,  2NHJ.  Ou2I2. —  Only  one  double  iodide  could 
be  obtained  by  the  use  of  ammonium  iodide  and  cuprous  iodide 
in  widely  varying  proportions  in  hydriodic  acid  solutions. 
This  circumstance  agrees  with  the  observation  made  upon 
several  other  series  of  double  salts  studied  in  this  laboratory, 
that  the  number  of  double  salts  possible  decreases  from  the 
chlorides  to  the  iodides.  Two  separate  crops  gave  the  follow- 
ing results  upon  analysis : 

Found.  Calculated  for 

I.  II.  2NH4I.Cu2I2. 

Ammonium 5.84  5.95  5.36 

Copper 18.75  .  .  .  18.90 

Iodine 75.07  75.55  75.74 

99.66  100.00 

Summary.  —  The  double  salts  obtained  in  the  present  inves- 
tigation are  as  follows : 

2  : 1  Type.  1  :  1  Type.  2  :  3  Type. 

4NH4Cl.Cu2Cl2  4NH4C1.3Cu2Cl2 

4NH4Br.Cu2Br2       2NH4Br.Cu2Br2.H20  

2NH4I.CuA  

The  two  bromides  are  apparently  new  compounds,  while  a 
formula  without  water  has  been  given  to  Saglier's  iodide.  The 
compound,  NH4Cl.Cu2Cl2,  of  Deherain  probably  does  not 
exist. 

It  was  hoped  that  ammonium-cuprous  salts  of  other  types, 
corresponding  to  the  caesium-cuprous  salts  described  by  one  of 
us,*  would  be  found,  but  such  has  not  been  the  case,  and  there 

*  Amer.  Jour.  Sci.,  xlvii,  96. 


DOUBLE  HALOGEN  SALTS.  389 

is  no  correspondence  between  the  two  series.  The  view 
advanced  in  the  article  just  mentioned,  that  the  formula 
4NH4C1.3Cu2Cl2  might  be  considered  somewhat  doubtful  on 
account  of  its  complexity  and  because  its  variation  from  the 
1 :  2  type  is  slight,  seems  to  have  been  unfounded. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
June,  1895. 


ON  THE  DOUBLE  FLUORIDES   OF   CESIUM 
AND   ZIRCONIUM.* 

BY  H.  L.   WELLS  AND  H.  W.  FOOTE. 

IN  connection  with  his  comprehensive  work  on  zirconoflu- 
orides,  Marignacf  has  investigated  the  double  fluorides  of 
zirconium  with  ammonium,  sodium,  and  potassium,  and  since 
the  corresponding  caesium  salts  have  never  been  investigated, 
we  have  undertaken  a  study  of  them. 

The  following  table  gives  Marignac's  ammonium  and  potas- 
sium salts,  together  with  those  which  we  have  prepared  with 
caesium : 

3  : 1  Type.         2  : 1  Type.         1  : 1  Type.  2  :  3  Type. 

3NH4F.ZrF4      2NH4F.ZrF4        

3KF.ZrF4          2KF.ZrF4         KF.ZrF4.H20  

2CsF.ZrF4        CsF.ZrF4.H20        2CsF.3ZrF4.2H20 

The  analogy  between  two  types  of  caesium  and  potassium 
salts  is  complete,  while  one  type  varies  in  each  series.  No 
evidence  has  been  found  that  caesium,  in  this  case,  forms  a 
greater  variety  of  compounds  than  potassium. 

The  symmetrical  arrangement  of  the  vacancies  in  the  table, 
where  no  salts  have  been  discovered,  indicates  that  alkaline 
fluorides  of  lower  molecular  weight  combine  with  a  relatively 
smaller  number  of  molecules  of  zirconium  fluoride,  while  those 
of  higher  molecular  weight  combine  with  a  greater  number  of 
such  molecules. 

The  2  :  1  type  is  the  only  one  occurring  in  all  three  series. 
This  is  the  common  and  usually  the  only  type  of  double  halo- 
gen salts  formed  by  tetravalent  elements ;  hence  its  occurrence 
in  all  cases  was  to  be  expected.  The  single  sodium  salt 

*  Amer.  Jour.  Sci.,  1, 1896.  f  Ann.  Chira.  Phys.,  Ill,  Ix,  257. 


DOUBLE  FLUORIDES  OF  CAESIUM,  ETC.  391 

described  by  Marignac,  5NaF.2ZrF4,  does  not  correspond  to 
any  of  the  compounds  in  the  above  table,  but  it  is  to  be 
noticed  that  the  composition  corresponding  to  this  formula 
varies  but  little  from  that  required  for  2NaF.ZrF4.  Although 
Marignac's  work  on  this  salt  was,  as  usual,  very  thorough  and 
careful,  it  seems  possible  that  his  products  may  have  been  the 
2  :  1  salt  containing  a  small  amount  of  some  impurity,  possibly 
a  3  :  1  compound. 

Marignac  described  the  salts  Mn2ZrFf,.6H2O,  Cd2ZrF8. 
6H2O,  Zn2ZrF8.12H2O,  and  Cu2ZrF8.12H2O,  all  of  which  cor- 
respond to  a  4  :  1  type  which  has  not  been  obtained  with  the 
alkali  metals.  This  type  and  those  given  in  the  preceding 
table  make  five  varieties  of  zirconofluorides,  one  of  which  has 
been  discovered  in  the  present  investigation. 

The  materials  used  for  the  preparation  of  the  caesium  salts 
under  consideration  were  carefully  purified  by  ourselves. 
Hydrofluoric  acid  was  made  from  perfectly  pure  fluor-spar 
and  sulphuric  acid,  using  a  platinum  still  and  redistilling  the 
product.  Caesium  carbonate,  purified  by  the  method  described 
by  one  of  us,*  was  used  in  preparing  the  fluoride.  Zircon  was 
used  as  the  source  of  zirconium.  The  crude  hydroxide  was 
conveniently  obtained  by  fusing  the  finely  pulverized  mineral 
with  four  parts  of  sodium  carbonate,  treating  the  resulting 
mass  with  hydrochloric  acid,  evaporating  with  an  excess  of 
sulphuric  acid  until  the  latter  fumed,  taking  up  with  water, 
filtering  and  precipitating  with  ammonia.  For  purifying  the 
zirconia,  the  method  of  Mitchell  which  has  been  advocated  by 
Baskerville  f  was  found  convenient.  This  consists  in  dissolv- 
ing the  zirconium  hydroxide  in  hydrochloric  acid,  nearly 
neutralizing  with  ammonia,  adding  a  strong  solution  of  sul- 
phur dioxide  and  boiling.  The  precipitate,  which,  from  the 
results  of  Venable  and  Baskerville,  \  appears  to  be  a  basic 
zirconium  sulphite,  can  readily  be  washed  free  from  iron. 

The  double  salts  were  prepared  by  mixing  solutions  of  the 
two  fluorides  in  widely  varying  proportions,  in  the  presence 

*  Amer.  Jour.  Sci.,  xlvi,  188.  t  Jour.  Amer.  Chem.  Soc.,  xvi,  475. 

J  Ibid.,  xvii,  448. 


392  ON  THE  DOUBLE  FLUORIDES  OF 

of  more  or  less  hydrofluoric  acid,  evaporating  to  the  proper 
point,  and  cooling. 

When  csesium  fluoride  is  in  excess,  even  with  very  small 
amounts  of  zirconium  fluoride,  the  salt  2CsF.ZrF4,  is  formed. 
It  crystallizes  in  rather  large,  simple  hexagonal  plates,  showing 
negative  double  refraction,  and  it  can  be  recrystallized  un- 
changed from  water. 

When  a  larger  proportion  of  zirconium  fluoride  is  used,  the 
salt  CsF.ZrF4.H2O  is  obtained.  This  forms  monoclinic  crys- 
tals elongated  in  the  direction  of  the  b  axis,  and  with  faces 
which  are  usually  too  rough  for  accurate  measurement.  This 
salt  also  can  be  recrystallized  unchanged  from  water. 

With  a  large  excess  of  zirconium  fluoride  extremely  small, 
difficultly  soluble  crystals  of  the  salt  2CsF.3ZrF4.2H2O  are 
produced.  The  small  crystals  have  a  slight  action  upon  polar- 
ized light,  but  their  form  could  not  be  made  out.  It  does  not 
recrystallize  from  water  in  a  pure  condition,  the  product  being 
mixed  with  the  1  :  1  salt. 

To  determine  csesium  and  zirconium,  the  fluorides  were  con- 
verted into  sulphates,  then  zirconium  was  separated  from 
csesium  by  the  use  of  ammonia,  and  zirconium  oxide  and 
csesium  sulphate  were  finally  weighed.  In  order  to  determine 
fluorine  a  separate  portion  was  dissolved  in  water,  zirconium 
hydroxide  was  precipitated  with  ammonia,  sodium  carbonate 
was  added  in  slight  excess  to  the  filtrate,  and  all  the  ammonia 
was  removed  by  evaporation.  To  the  hot  solution  calcium 
nitrate  was  added,  and  the  resulting  precipitate,  after  ignition, 
was  cautiously  treated  with  dilute  formic  acid  until,  after 
evaporation  on  the  water-bath,  a  further  addition  of  the  acid 
produced  no  effervescence.  The  calcium  fluoride  finally 
remaining  after  a  final  evaporation  was  washed,  ignited,  and 
weighed.  The  results  of  the  fluorine  determinations  were 
invariably  somewhat  low. 

The  substitution  of  formic  acid  for  the  acetic  acid  usually 
used  in  removing  calcium  carbonate  from  the  fluoride  was  sug- 
gested by  the  greater  volatility  of  the -first  acid  and  the  solu- 
bility of  its  calcium  salt.  We  have  found  the  modification  to 


CAESIUM  AND  ZIRCONIUM.  393 

be  an  improvement  as  far  as  convenience  is  concerned,  but  we 
are  not  yet  prepared  to  say  that  it  is  more  accurate  than  the 
old  method. 

Water  was  determined  by  heating  the  substance  in  a  boat 
behind  a  layer  of  dry  sodium  carbonate  in  a  combustion  tube, 
and  collecting  and  weighing  it  in  a  calcium-chloride  tube. 

The  following  analyses  of  separate  crops  were  made : 


Calculated. 

56.60 
19.15 
24.25 


The  small  amount  of  water  found  in  the  analyses  was  evi- 
dently mechanically  included,  for  under  the  microscope  bub- 
bles of  mother-liquor  could  be  occasionally  seen  within  the 
crystals. 

CsF.ZrF4.HtO. 


ZCsF.ZrFt. 

Found. 

Caesium      .    . 
Zirconium 
Fluorine    .     . 
Water    . 

A. 

.     .    56.41 
.    .     18.94 
.     .     22.73 
1.63 

B. 

19.30 
22.75 

0.98 

c. 
55.51 
19.16 

0.97 

JTOI 

A. 

ma. 
B. 

Calculated. 

Caesium     .     . 



38.44 

39.58 

Zirconium 

.     .     27.19 

27.11 

26.79 

Fluorine    .     . 

.     .    27.24 

27.52 

28.27 

Water  . 

6.27 

5.20 

5.36 

JPOl 

A. 

ma. 
B. 

Calculated. 

Caesium     . 

.    .    .    32.03 

30.56 

31.74 

Zirconium 

.     .     .    32.45 

33.48 

32.22 

Fluorine    . 

.    .    .    31.09 

30.43 

31.74 

Water  . 

4.40 

3.96 

4.30 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
July,  1895. 


ON  CERTAIN   DOUBLE   HALOGEN  SALTS   OF 
CAESIUM   AND   RUBIDIUM.* 

BY  H.  L.  WELLS  AND  H.  W.  FOOTE. 

1.    The  Complicated  Rubidium- Antimony  Chloride. 

REMSEN  and  SAUNDERS f  have  described  a  salt  to  which 
they  gave  the  formula  23RbC1.10SbCl3  as  the  most  probable 
one.  Wheeler,  J  working  in  this  laboratory,  confirmed  Remsen 
and  Saunders'  results,  and  discovered  besides  an  analogous 
bromide,  to  which  the  probable  formula  23RbBr.lOSbBr3  was 
given.  Remsen  and  Brigham  §  prepared  the  salt  23RbCL 
lOBiClg.  Herty  ||  has  since  described  the  two  potassium  salts 
23KC1.10SbCl8  and  23KBr.lOSbBr8.27H2O,  and  some  mixtures 
of  these  two  salts. 

In  view  of  all  this  work,  there  can  scarcely  be  a  doubt  as  to 
the  existence  of  a  type  of  salts  with  a  somewhat  complicated 
ratio,  but  in  view  of  the  fact  that  this  complicated  ratio  23  : 10 
is  apparently  an  exception  to  the  simplicity  of  composition  of 
all  other  carefully  investigated  double  halogen  salts,  the  sub- 
ject seemed  worthy  of  some  further  investigation.  For  the 
purpose  we  have  studied  only  the  rubidium-antimony  chloride 
of  Remsen  and  Saunders,  as  this  salt  is  readily  prepared  and 
is  capable  of  repeated  recrystallization  from  hydrochloric  acid 
solution. 

The  possibility  suggested  itself  that  the  product  might  con- 
sist of  two  simpler  salts  of  similar  or  identical  crystalline  form, 
which  were  capable  of  crystallizing  together,  and  that  previous 
investigators  had  made  use  of  conditions  which  resulted  in 
obtaining  a  constant  mixture  of  two  such  salts.  Although 

*  Amer.  Jour.  Sci.,  Ill,  1897.  t  Ibid.,  xiv,  155. 

t  Ibid.,  xlvi,  269.  §  Amer.  Chem.  Jour.,  xiv,  174. 

||  Ibid.,  xvi,  490. 


CERTAIN  DOUBLE  HALOGEN  SALTS.  395 

this  supposition  had  scarcely  any  probability  in  view  of  the 
existence  also  of  the  rubidium-antimony  bromide  and  of  the  two 
potassium  salts,  we  have  put  the  question  to  test  by  repeatedly 
recrystallizing  the  salt,  using  not  only  ordinary  dilute  hydro- 
chloric acid  for  this  purpose,  but  also  more  dilute  and  much 
more  concentrated  acid  and  also  an  alcoholic  hydrochloric  acid 
solution.  As  will  be  seen  from  the  analyses,  given  beyond,  no 
variation  in  composition  could  be  detected  by  the  use  of  these 
widely  varying  solvents  for  recrystallization,  and  it  therefore 
appears  impossible  that  the  salt  can  be  a  mixture. 

As  a  starting-point,  we  used  a  solution  in  hydrochloric  acid 
containing  the  constituents  RbCl  and  SbCl3  in  the  exact  molecu- 
lar proportion  23  : 10.  Product  A  was  the  first,  B  the  third, 
and  C  the  fifth  recrystallization  from  pure  dilute  hydrochloric 
acid.  The  product  D  was  obtained  by  adding  concentrated 
hydrochloric  acid  to  a  nearly  saturated  warm  solution  of  the 
salt  in  dilute  hydrochloric  acid.  E  was  obtained  from  a  very 
strong  hydrochloric  acid  solution  formed  by  passing  a  rapid 
current  of  hydrogen  chloride  gas  into  the  solution  as  it  cooled. 
F  was  obtained  by  recrystallizing  the  salt  from  hydrochloric 
acid,  which  was  kept  as  dilute  as  it  could  be  without  producing 
the  basic  double  salt  to  be  described  beyond.  G  was  a  product 
obtained  by  recrystallizing  the  salt  from  a  mixture  of  equal 
volumes  of  dilute  hydrochloric  acid  and  alcohol. 

The  two  products  obtained  from  concentrated  hydrochloric 
acid  solution  had  a  pale  yellow  color,  while  the  others  were  all 
white.  The  crystals  were  usually  well-formed  six-sided  plates 
which  showed  no  definite  optical  properties. 

The  analyses  of  the  various  products  are  as  follows : 

Rubidium.  Antimony.  Chlorine. 

A 39.23  23.85  37.01 

B 39.23  23.84  36.99 

C 23.91 

D 39.25  23.98 

E 39.31  23.89 

F 39.03  23.86 

G 39.11  23.90 

Average      ....  39.19  23.89  37.00 


396  CERTAIN  DOUBLE  HALOGEN  SALTS 

Method  of  Analysis.  —  For  the  determination  of  antimony 
and  rubidium,  a  portion  of  about  half  a  gram  was  dissolved 
in  water  and  enough  hydrochloric  acid  to  prevent  antimony 
oxychloride  from  precipitating.  The  solution  was  heated 
to  boiling  and  hydrogen  sulphide  passed  in.  The  solution  was 
then  cooled  and  the  antimony  sulphide  filtered  on  a  Gooch 
crucible  and  washed  with  water  and  with  alcohol.  The  crucible 
was  then  slowly  heated  to  230°  and  cooled  in  an  oven  filled 
with  carbonic  acid.  The  precipitate  was  weighed  as  Sb2S3. 
The  filtrate  containing  rubidium  was  evaporated  with  sulphu- 
ric acid,  and  the  residue  ignited  in  a  stream  of  air  containing 
ammonia  and  weighed  as  Rb2SO4.  Chlorine  was  determined 
by  dissolving  a  separate  portion  in  water  acidified  with  tartaric 
and  nitric  acids  and  precipitating  with  silver  nitrate.  This 
was  allowed  to  stand  for  some  time,  and  the  precipitate  was 
then  collected  on  a  Gooch  crucible  and  weighed.  .The  methods 
used  are  almost  identical  with  those  of  Wheeler. 

The  accuracy  of  the  antimony  determination  was  checked  in 
the  following  manner.  The  salt  Cs3Sb2Cl9  was  prepared  from 
very  pure  materials  and  carefully  recrystallized,  and  antimony 
determined  by  the  above  method.  The  per  cent  of  antimony 
is  nearly  the  same  as  in  the  rubidium  antimony  salt  under 
consideration.  The  following  results  were  obtained : 

I.  II.  III.  IV. 

Per  cent  Sb  found      .    .    25.37       25.42       25.43       25.44 
"         "  calculated   .    25.13        

The  atomic  weights  used  in  all  the  calculations  were  Rb,  85.43 ; 
Sb,  120.43;  Cl,  35.45;  S,  32.07;  Ag,  107.92;  Cs,  132.89. 

Since  the  method  used  for  the  determination  x)f  antimony 
gives  results  which  are  slightly  too  high,  we  believe  that  a 
deduction  of  the  average  error  0.25  per  cent  from  the  antimony 
found  in  the  analyses  of  the  rubidium  salt  will 'give  a  result 
which  is  nearer  the  truth. 

Rb.  Sb.  Cl. 

Average  previously  given     «     .  39.19  23.89  37.00 

Average  with  correction  for  Sb  39.19  23.64  37.00 

Calculated  for  Rb28Sb10Cl6S    .    ;  38.92  23.86  37.22 

Calculated  for  Rb7Sb8Cl16      .     .  39.18  23.66  37.16 


OF  CAESIUM  AND  RUBIDIUM.  397 

It  may  be  noticed  that  the  results  agree  rather  more  satis- 
factorily with  the  formula  7RbC1.3SbCl8  than  with  the  more 
complicated  one  advanced  by  Remsen  and  Saunders.  The 
differences  between  these  formulae  are,  however,  so  slight  that 
it  is  probably  entirely  impossible  to  decide  between  them  by 
means  of  chemical  analysis,  the  ratio  Rb :  Sb  being  230 : 100 
in  one  case,  and  in  the  other  233  : 100.  However,  since  it  is 
customary  to  use  the  simplest  applicable  formula  for  a  chem- 
ical compound,  we  propose  the  formula  7RbC1.3SbCl8  for  this 
salt  and  corresponding  formulas  for  other  salts  of  this  series. 
Herty's  hydrous  salt,  to  which  he  gave  the  formula  23KBr. 
10SbBr3.27H2O,  agrees  well  with  the  formula  7KBr.3SbBr8 
8H2O.  It  must  be  admitted  that  the  7 :  3  ratio  is  an  unusually 
complicated  one,  but  it  is  far  simpler  than  23 : 1 0,  and  is 
scarcely  a  marked  exception  to  the  general  simplicity  of  double 
halogen  salts. 

2.  A  Rubidium-Antimony  Oxy chloride,  2RbCl.SbCl8.SbOCl. 

In  attempting  to  recrystallize  the  salt  7RbC1.3SbCl8  from 
very  dilute  hydrochloric  acid,  just  enough  to  prevent  the  forma- 
tion of  antimony  oxychloride,  this  new  salt  was  obtained  in  the 
form  of  short  colorless  prisms  possessing  a  rather  high  lustre. 
It  can  be  recrystallized  from  very  dilute  hydrochloric  acid. 

The  following  results  were  obtained  from  analyses  of 
separate  crops : 

Found.  Calculated  for 

I.  H.  2RbC1.8bCl8.8bOCL 

Kb 26.54  26.68  26.68 

Sb 37.58  37.36  37.61 

Cl 32.75  32.80  33.21 

O  (by  diff.)  .     .    .  3.13  3.16  2.50 

It  is  interesting  to  notice  that  Benedict  *  has  described  the 
potassium  salt  2KCl.SbCl3.SbOCl,  which  corresponds  exactly 
to  this  rubidium  compound. 

3.    The  Ccesium- Bismuth  Chlorides  and  Iodides. 

The  double  chlorides  of  bismuth  with  caesium  have  been 
described  by  Remsen  and  Brigham.  -f  These  authors  did  not 

*  Proc.  Amer.  Acad.,  xxix,  212.  *  Amer.  Chem.  Jour.,  xiv,  179. 


398  CERTAIN  DOUBLE  HALOGEN  SALTS 

state,  however,  how  widely  the  conditions  had  been  varied,  and 
we  have  repeated  the  work,  varying  the  proportions  of  caesium 
and  bismuth  as  much  as  possible,  and  have  found  exactly  the 
same  salts  as  described  by  them.  These  salts  are, 

3CsCl.BiCls 
3CsC1.2BiCl3 

SCsCLBiCls.  —  This  salt  forms  in  colorless  plates  when  50  g. 
of  caesium  chloride  are  mixed  in  hydrochloric  acid  solution 
with  from  1-25  g.  of  bismuth  chloride.  The  analyses  were 
made  on  samples,  dried  but  a  short  tune  in  the  air,  which 
apparently  contained  a  little  mechanically  included  water. 
The  following  results  were  obtained : 

Found.  Calculated  for 

I.  II.  3CsCl.BiCl3. 

Bi 24.80        24.47  25.36 

Cs 47.94         .  .  .  48.66 

Cl 25.98 

3CsCl.2BiCh.  —  When  50  g.  of  bismuth  chloride  are  mixed 
with  from  1-80  g.  of  caesium  chloride,  the  salt  3CsC1.2BiCl3 
crystallizes  in  light  yellow  needles,  sometimes  broadened  and 
looking  like  plates  and  again  much  shorter  and  thicker. 

The  following  analyses  were  made : 

Pound.  Calculated  for 

I.  II.  3CsC1.2BiCl3. 

Bi 36.99        36.58  36.67 

Cs 34.69        34.94  35.17 

Cl 28.16 

3C8L2Bil#  Ccesium-Bismuth  Iodide. 

We  could  obtain  only  one  double  iodide  of  bismuth  and 
caesium,  although  the  proportions  of  caesium  and  bismuth  were 
varied  greatly.  The  salt  formed  as  a  crystalline  precipitate, 
difficultly  soluble  especially  in  an  excess  of  caesium  iodide, 
when  1  g.  of  bismuth  iodide  was  added  to  50  g.  of  caesium 
iodide  and  when  1  g.  of  caesium  iodide  was  added  to  50  g.  of 
bismuth  iodide.  With  an  excess  of  caesium,  the  color  was  a 
bright  red,  while  with  an  excess  of  bismuth  the  color  was  more 
of  a  reddish  brown. 


OF  CESIUM  AND  RUBIDIUM.  399 

Methods  of  Analysis.  —  The  methods  here  given  were  used 
in  both  the  double  chlorides  and  iodide  of  bismuth. 

Halogens  were  determined  as  the  silver  salts  being  precipi- 
tated from  a  solution  acidified  with  tartaric  and  nitric  acids 
and,  after  standing,  filtered  and  weighed  on  a  Gooch  crucible. 
As  Remsen  and  Brigham  had  mentioned  a  difficulty  in  deter- 
mining bismuth,  we  made  a  few  determinations  of  it  in  Bi2O8, 
which  was  made  by  precipitating  BiONO8  with  water  from  a 
nitric  acid  solution  of  Bi(NO8)8,  and  heating  the  precipitate  to 
constant  weight  in  a  platinum  dish.  The  method  finally 
adopted  was  to  dissolve  the  substance  in  water  slightly  acidi- 
fied with  hydrochloric  acid  and  precipitate  Bi2S8  from  the  cold 
solution  with  hydrogen  sulphide.  The  precipitate  was  filtered 
and  immediately  dissolved  in  nitric  acid  and  digested  for  some 
time  on  the  water  bath  until  completely  decomposed.  The 
sulphur  was  filtered  off  and  the  filtrate,  diluted  to  about  300- 
400  c.  c.,  was  heated  and  ammonium  carbonate  added  in  slight 
excess.  It  was  placed  on  the  water  bath  for  an  hour  or  two, 
until  the  liquid  had  become  nearly  clear  and  the  excess  of 
ammonium  carbonate  had  been  driven  off,  and  it  was  then  fil- 
tered on  a  Gooch  crucible  and  ignited  strongly  over  a  Bunsen 
burner  and  weighed  as  Bi2O3. 

Two  determinations  on  Bi2O8  gave  the  following  results  : 

I  Amt.  Bi208  taken  =  0.1979  g.       Amt.  Bi208  found  =  0.1974  g. 
II      «        «        «      =  0.3604  g.         "        «         "      =  0.3617  g. 

The  filtrate  from  the  bismuth  precipitation  was  evaporated 
with  sulphuric  acid  and  ignited  in  a  stream  of  air  containing 
ammonia.  The  residue  was  weighed  as  Cs2SO4. 

The  results  obtained  from  the  analysis  of  the  double  iodide 
were  as  follows  : 

Found.  Calculated  for 

I.  II. 


Bi    .....    21.34        21.15  21.25 

Cs    .....    20.75        20.31  20.38 

I      ........         58.02  58.37 

SHEFFIELD  CHEMICAL  LABORATOBY, 
January,  1897. 


ON  THE  DOUBLE  FLUORIDES   OF  ZIRCONIUM 
WITH  LITHIUM,  SODIUM,  AND  THALLIUM.* 

BY  H.  L.  WELLS  AND  H.  W.  FOOTE. 

IN  a  previous  article  f  we  have  described  the  caesium-zir- 
conium fluorides,  and  upon  comparing  these  with  the  corre- 
sponding ammonium  and  potassium  salts,  which  had  been 
previously  described  by  Marignac,  J  it  was  observed  that  the 
types  of  salts  formed  varied  with  the  molecular  weights  of  the 
alkaline  fluorides  in  an  interesting  manner.  The  fluorides  of 
smaller  molecular  weight  gave  types  with  a  larger  relative 
number  of  these  molecules,  while  the  fluorides  of  higher  molec- 
ular weights  combined  with  more  zirconium  fluoride  than  the 
others.  This  relation  is  made  clear  from  the  following  table, 
which  was  given  in  the  previous  article  referred  to : 


2:3Type. 


3:lType. 

3NH4F.ZrF4 
3KF.ZrF4 

2  :  1  Type. 

2NH4F.ZrF4 
2KF.ZrF4 
2CsF.ZrFA 

1  :  1  Type. 

KF.ZrF4 
CsF.ZrF, 

2CsF.3ZrF4.2H20 

The  present  investigation  was  undertaken  with  the  view, 
in  the  first  place,  of  testing  the  apparent  rule  with  lithium 
fluoride,  which  has  a  lower  molecular  weight  than  the  fluorides 
previously  experimented  upon.  Our  expectations  were  real- 
ized by  the  preparation  of  the  salt  4LiF.ZrF4.|H2O.  The  salt 
2LiF.ZrF4  was  also  obtained,  but,  in  spite  of  a  careful  search, 
no  intermediate  3  :  1  salt  could  be  discovered.  The  following 
table,  giving  the  lithium,  potassium,  and  caesium  salts,  shows  a 
perfectly  symmetrical  gradation  in  types  according  to  the 

*  Amer.  Jour.  Sci.,  Ill,  1897.  t  Ibid.,  IV.  i,  18. 

J  Ann.  Chim.  Phys.,  ix,  257. 


DOUBLE  FLUORIDES   OF  ZIRCONIUM. 


401 


atomic  weights  of  the  alkali  metals,  except  that  the  intermedi- 
ate lithium  salt  is  missing. 


Type. 

4:  1 
3  :  1 

Lithium  Salts. 

4LiF.ZrF4.§H20 

2:1 
1  :  1 

2LiF.ZrF4 

2:3 

Potassium  Salts. 
(Marignac.) 


3KF.ZrF4 
2KF.ZrF4 


Caesium  Salts. 


2CsF.ZrF4 


KF.ZrF4.H20      CsF.ZrF4.H20 


2CsF.3ZrF4.2H20 


Marignac's  two  ammonium  salts,  3  :  1  and  2  :  1,  also  enter 
the  series  symmetrically. 

We  have  investigated  also  the  thallous-zirconium  fluorides, 
since  the  high  atomic  weight  of  thallium  led  us  to  expect  that 
it  would  possibly  yield  a  series  of  salts  symmetrical  with  those 
of  the  alkali  metals  with  a  still  higher  ratio  of  zirconium  than 
was  the  case  with  caesium.  Such  was  not  the  case,  however. 
The  salts  discovered  were : 

3TlF.ZrF4,  5TlF.3ZrF4.H20,  TlF.ZrF4,  and  TlF.ZrF4.H20. 

Two  of  these  three  types  of  thallous  salts  correspond  to 
types  of  alkali-metal  salts,  while  one  type,  the  5  :  3,  is  a  new 
one,  but  the  series  is  not  symmetrical  with  the  others  accord- 
ing to  the  atomic  weights. 

Since  Marignac  had  described  but  one  sodium-zirconium 
fluoride,  5NaF.2ZrF4,  and  since  this  differs  from  all  other 
alkaline  zirconium  fluorides,  we  have  undertaken  a  new  inves- 
tigation of  the  sodium  salts.  As  a  result,  we  have  fully  con- 
firmed Marignac's  results  as  to  the  5  :  2  salt,  which  is  the  one 
most  readily  obtained,  and  we  have  succeeded  in  preparing  a 
new  salt,  2NaF.ZrF4,  which  corresponds  to  the  most  usual 
type  of  double  halogen  salts  of  tetravalent  elements.  It  is 
evident,  however,  that  the  sodium  salts,  like  those  of  thallium, 
do  not  form  a  symmetrical  series  with  the  others. 

The  following  table  gives  a  list  of  the  sodium  and  thallium 
salts,  and  shows  the  positions,  "X,"  of  the  other  compounds 
prepared  by  Marignac  and  ourselves. 

26 


402  DOUBLE  FLUORIDES   OF  ZIRCONIUM 


Lithium     Ammonium          godium         Potassium      Caesium  Thallium 

Type.        Salts.  Salts.  galt8.  ,     ^alts.  Salts.  Salts. 


4:1       X  

3  .  1       ..  X  X  ..       3TlF.ZrF4 

2  •  1       X  X      2NaF.ZrF4       X  X          

5.3  5TlF.3ZrF  4H20 

<TlF.ZrF4 

\  TlF.ZrF4.H20 

2:3 X          

While  our  investigation  has  shown  that  the  rule  for  the 
variation  of  the  types  with  the  atomic  weights  applies  only 
partially  to  the  zirconium  double  fluorides,  we  have  shown  at 
least  that  the  variety  of  types  is  remarkable,  and  it  is  also 
noticeable  that  the  ratios  are  nearly  the  simplest  that  can  exist 
in  such  number  between  the  extreme  limits  4  :  1  and  2  :  3. 

Preparation.  —  Thallium  fluoride  was  prepared  by  dissolv- 
ing the  metal  in  sulphuric  acid,  adding  an  excess  of  baryta 
water,  filtering  and  passing  carbonic  acid  into  the  hot  solution. 
The  filtrate  from  this  precipitation  was  evaporated  and  treated 
with  hydrofluoric  acid  in  excess.  The  salts  were  prepared  by 
mixing  the  acid  solutions  of  the  fluorides  in  varying  propor- 
tions, evaporating  and  cooling  to  crystallization.  The  salts 
were  then  removed  and  pressed  between  filter  papers  till  dry. 
In  all  cases  they  were  stable  in  the  air. 

Method  of  Analysis.  —  Zirconium  and  the  alkalies  were 
determined  by  evaporating  the  salt  with  sulphuric  acid  to 
drive  off  hydrofluoric  acid,  precipitating  zirconium  hydroxide 
with  ammonia  and  weighing  ZrO2.  The  filtrate  was  evapo- 
rated to  dryness  and  the  alkali  determined  as  sulphate,  either 
by  igniting  with  ammonium  carbonate  or  heating  in  a  current 
of  air  containing  ammonia.  When  thallium  was  present,  the 
fluoride  was  dissolved  in  water,  a  little  sulphurous  acid  added 
to  make  sure  that  the  thallium  was  all  in  the  univalent  condi- 
tion, and  the  zirconium  precipitated  with  ammonia.  The  pre- 
cipitate needed  to  be  very  thoroughly  washed.  The  filtrate 
was  evaporated  nearly  or  quite  to  dryness  to  remove  free 


WITH  LITHIUM,  SODIUM,  AND   THALLIUM.        403 

ammonia,  diluted  to  a  volume  of  about  100  c.  c.,  heated  to 
boiling  and  potassium  iodide  added  in  excess  to  precipitate 
thallium  iodide.  This  was  collected  on  a  Gooch  crucible, 
washed  with  eighty  per  cent  alcohol,  dried  at  100°  C.  and 
weighed.  Fluorine  was  determined  by  the  ordinary  calcium 
fluoride  method  after  precipitating  zirconium  with  ammonia 
and  removing  ammonium  salts  by  evaporation  with  sodium 
carbonate.  Water  was  determined  by  heating  the  salt  in  a 
combustion  tube  behind  a  layer  of  dry  sodium  carbonate  and 
collecting  the  water  in  a  calcium  chloride  tube. 

Salts  of  Lithium. 

2LiF.ZrJF4.  —  This  salt  forms  when  from  0.7  g.  to  2  g.  of 
lithium  fluoride  are  added  to  20  g.  of  zirconium  fluoride.  The 
crystals  are  hexagonal,  showing  prism  and  pyramid  and  rarely 
a  basal  plane.  In  appearance,  they  are  very  much  like  crystals 
of  quartz  from  Herkimer  County,  New  York,  but  they  are 
very  small.  On  recrystallizing,  the  4  :  1  salt  was  formed. 

Separate  crops  were  analyzed  with  the  following  results : 


Li 
Zr 

F 


Found. 

I               n. 
6.03          6.39 

Calculated  for 
Li2ZrFe. 

6.42 

41.81        41.64 

41.28 

51.62 

52.30 

.  —  This  was  the  most  unsatisfactory  salt 
obtained,  though  it  seems  undoubtedly  to  establish  the  4  :  1 
type.  As  lithium  fluoride  is  very  insoluble,  only  a  compara- 
tively small  amount  could  be  dissolved  in  zirconium  fluoride, 
and  apparently  we  could  not  go  far  enough  toward  the  lithium 
end  to  get  the  salt  in  pure  condition.  It  formed  in  a  crust 
ordinarily,  and  the  crystals  were  very  small.  Under  the  micro- 
scope, no  mixture  with  another  salt  could  be  found  in  the 
crops  analyzed.  Once,  however,  it  was  obtained  mixed  with 
the  2  :  1  salt,  as  seen  under  the  microscope,  showing  there 
could  probably  be  no  intermediate  salt.  Various  conditions 
were  tried,  and  crops  were  obtained  from  both  hot  and  cold 


404  DOUBLE  FLUORIDES  OF  ZIRCONIUM 

solutions.  It  forms  when  5  to  7  g.  of  lithium  fluoride  are 
mixed  with  20  g.  of  zirconium  fluoride.  On  recrystallizing, 
lithium  fluoride  is  precipitated. 

Following  are  the  results  of  the  analyses: 


I 

II 

III 

IV 

V 


Salts  of  Sodium. 

2NaF.ZrF4.  —  This  salt  crystallizes  in  very  minute  crystals 
of  hexagonal  outline,  coming  down  in  a  crust  when  from  one 
to  two  parts  of  sodium  fluoride  are  added  to  fourteen  parts  of 
zirconium  fluoride.  The  salt  does  not  recrystallize.  The  fol- 
lowing results  were  obtained  from  separate  crops.  The  water 
was  probably  mechanically  included. 


Li. 

.    .     .    9.54 

Zr. 

33.14 

H30. 

4.83 

F. 

4.93 

[   

.    .     .    9.79 

33.30 

4.35 

53.16 

33.23 

33.02 

Iculated  for  Li,ZrF8.§ 

H20  .  .    9.93 

31.91 

4.26 

53.90 

Found.  Calculated  for 

I.  H. 


Na    .  .  .  18.66  18.41  18.40 

Zr     .  .  .  34.78  36.21  36.00 

H20  .  .  .  1.96  0.50 

F*     .  .  .  44.60  44.88  45.60 


.  —  Marignac  has  previously  described  this  salt, 
which  comes  down  under  wide  conditions  in  very  good  crys- 
tals and  recrystallizes  easily.  Prof.  L.  V.  Pirsson  has  kindly 
examined  the  crystals  and  made  the  following  report  : 

"  The  crystals  show  good  sharp  forms,  but  are  very  small. 
They  appear  distinctly  orthorhombic  in  habit,  consisting  in  the 
main  of  rather  stout  prisms,  made  up  of  two  prismatic  planes, 
m  and  m',  and  terminated  by  a  rather  steep  brachydome.  In 
another  habit,  which  is  rarer,  the  front  pinacoid,  a,  is  broadly 
developed,  while  the  prisms  are  very  small  ;  this  type  also 
shows  at  times  a  pyramid,  p.  The  plane  of  the  optic  axes  lies 

*  By  difference. 


WITH  LITHIUM,   SODIUM,  AND   THALLIUM.        405 

in  the  base  and  a  =  c,  b  =  %,c  =  b.  The  optic  angle  is  large, 
and  it  could  not  be  told  whether  a  or  b  was  the  acute  bisectrix. 
The  double  refraction  is  very  low.  The  crystals  in  their  form 
strongly  recall  the  figures  of  chrysolite  (olivine)  shown  in  the 
mineralogies." 

The  analyses  gave  the  following  results  from  different  crops  : 


Found.  Calculated  for 

I.  II. 


Na  .....    21.15        21.09  21.23 

Zr   .....     33.63        33.55  33.22 

F*   .....    45.22        45.36  45.57 

Salts  of  Thallium. 

TlF.ZrF^O  and  TlF.ZrF^.  —  These  salts  crystallize  in 
somewhat  concentrated  solutions  when  one  part  of  thallium 
fluoride  is  mixed  with  three  or  four  parts  of  zirconium  fluoride. 
The  analyses  invariably  show  an  excess  of  zirconium  fluoride. 
The  hydrous  salt  crystallizes  in  needles,  if  the  solution  be 
cooled  before  precipitation  occurs.  If  the  solution  is  evapo- 
rated until  crystals  begin  to  form  and  then  cooled,  the  anhy- 
drous salt  deposits  in  minute  square  plates.  The  salt  gives 
the  5  :  3  type  on  recrystallizing.  The  following  results  were 
obtained  : 

Found.  Calculated  for 

I.  II.  TlZrF5.H20. 

50.05 

22.15 
23.37 
4.43 

Calculated  for 
TlZrFs. 

Tl    .....    50.16        49.91  52.37 

Zr    .....    23.86        24.08  23.17 

F     ........         24.32  24.46 

5TlF.3ZrFi.HtO.  —  This  salt  crystallizes  in  needles  when 
from  one  to  three  and  one-half  parts  of  thallium  fluoride  are 
added  to  one  part  of  zirconium  fluoride.  When  about  four 

*  By  difference. 


Tl 

....  48.43 

47.91 

Zr  . 

....  22.93 

23.16 

F  . 

23.17 

H20 

.   3.89 

4.80 

406  DOUBLE  FLUORIDES  OF  ZIRCONIUM. 

parts  of  thallium  fluoride  are  added,  the  same  salt  crystallizes 
in  a  different  habit,  forming  prisms  of  hexagonal  outline  which 
under  the  microscope  are  seen  to  be  twinned,  resembling  in 
this  respect  the  hexagonal-shaped  crystals  of  aragonite.  On 
recrystallizing,  both  habits  give  the  needle-shaped  crystals. 

The  following  analyses  were  made  of  the  two  kinds  of  crys- 
tals. A  rather  large  number  of  determinations  was  made  on 
account  of  the  existence  of  two  different  forms. 

TL  Zr.  H20,  P. 

I  ............    61.58    16.88    ...... 

II  ............    62.05    16.84    ...... 

III  ...........     61.37     17.14    1.40     .  .  . 

IV  ...........     61.58    16.88    1.17    19.31 

V  ............     61.74     17.04    1.42      .  .  . 

VI  .................     1.31      .  .  . 

VII  ...........    62.91     16.42    ...... 

Calculated  for  Tl6Zr8F17.H20     .     .    62.47    16.58    1.11     19.84 


^  —  Crystals  of  this  salt  form  in  brilliant  octa- 
hedra  when  one  part  of  zirconium  fluoride  is  added  to  from 
four  to  twenty  parts  of  thallium  fluoride.  It  is  easily  recrys- 
tallized. 

The  following  analyses  were  made  : 

Found.  Calculated  for 

I.  II.  TlsZrF7. 

Tl   .....    72.82        73.20  73.24 

Zr   .....     10.91        10.38  10.80 

F     .....    15.65         .  .  .  15.96 

SHEFFIELD  CHEMICAL  LABORATORY, 
January,  1897. 


ON  THE  CAESIUM  ANTIMONIOUS  FLUORIDES 

AND  SOME   OTHER  DOUBLE  HALIDES 

OF  ANTIMONY. 

BY  H.  L.  WELLS  AND  F.  J.  METZGER. 

WE  have  made  a  thorough  study  of  the  double  salts  formed 
by  caesium  fluoride  and  antimonious  fluoride  with  the  result 
that  five  compounds  have  been  prepared.  This  is  an  un- 
usual number  for  a  series  of  double  salts,  and  it  gives  a  good 
illustration  of  the  facility  with  which  caesium  forms  such 
compounds. 

The  salts  to  be  described  have  the  following  formulas : 

Type. 

1:3 CsF.3SbF8 

1:2 CsF.2SbF8 

4:7 4CsF.7SbF, 

1:1 CsF.SbF8 

2:1 2CsF.SbF8 

The  previously  described  antimonious  double  fluorides,  all 
of  which  were  prepared  by  Fliickiger,*  are  as  follows : 

Type. 

1:1...       KF.SbFs  ....  .... 

2:1    ...    2KF.SbF8        2LiF.SbF8        2NH4F.SbF8 
3:1...    3NaF.SbF8          ....  .... 

The  following  chlorides,  bromides,  and  iodides  have  been 
described : 

*  Pogg.  Ann.,  Ixxxvii,  245  (1852). 


408         CAESIUM  ANTIMONIOUS  FLUOEIDES  AND 

Type. 

1  :  2         BbC1.2SbCl3* 

3:4         3NH4I.4SbI8.9H2Ot 

1  :  1         NH4Cl.SbCl8 ;  *  NH4LSbI8.2H20 ;  §  KLSbI8H20  ;  § 

BbCLSbCl,  II 

(  3KI.2SbI,.3H20  ;  t  3NaI.2SbI,.12H,O  ;  t 
3:2      \  3NH4L2SbI8.3H|0 1  3RbC1.2SbCl8 ;  * 

(3RbBr.2SbBr8;*  3RbL2SbI8 ;  *  3CsC1.2SbCl81[ 

2  :  1         2NH4Cl.SbCl, ;  t  2NH4Cl.SbCl8.H20 ;  IT  2KClSbCl8 ;  ft 

2KCl.SbCl82H20  « 

1 :  3  §§     7EbC1.3SbCl3 ;  ||  7KbBr.3SbCl3  j  *  7KC1.3SbCl, ;  ||  || 
7KBr.3SbBr8.8H20  ||  || 

3  :  1     3NH4Cl.SbCl8.liH,0;  **  (3KCl.SbCl,) ;  **  3NaCl.SbCl8«* 

4  :  1     4NH4I.SbI8.3H2Ot 

Upon  comparing  the  caesium  double  fluorides  with  the  salts 
already  known,  it  is  to  be  noticed  that  two  types  of  the 
former,  1 :  3  and  4  :  7,  do  not  occur  among  the  latter,  and  that 
the  3:4,  3:2,  7:3,  3:1,  and  4  :  1  types  were  not  found 
among  the  csesium  antmionious  fluorides.  The  absence  of  a 
3  :  2  fluoride  is  remarkable,  since  the  salt  3CsC1.2SbCl3  is 
very  sparingly  soluble,  and  because  this  is  a  very  prominent 
type  among  the  chlorides,  bromides,  and  iodides.  It  is  evident 
that  a  close  relation  does  not  exist  between  the  caesium  anti- 
monious  fluorides  and  the  other  antimonious  double  halides, 
and  that  the  types  of  the  former  could  not  have  been  pre- 
dicted from  a  consideration  of  the  latter.  In  range,  the 

*  Wheeler,  Amer.  Jour.  Sci.,  (Ill),  xlvi,  269. 
t  Schaffer,  Pogg.  Ann.,  cix,  611. 
t  Deherain,  Compt.  rend.,  lii,  734. 
§  Nickles,  Ibid.,  li,  1097. 

||  Remsen  and  Saunders,  Amer.  Chem.  Jour.,  xlv,  152. 
If  Setterberg,  Of  versigt  K.  Vetensk-akad.  Forhandl.,  1882, 23 ;  Eemsen  and 
Saunders,  loc.  cit. 

**  Poggiale,  Compt.  rend.,  xx,  1180.  It  is  probable  according  to  Herty, 
Amer.  Chem.  Jour.,  xv,  81,  that  3KCl.SbCl3  does  not  exist. 

tt  Jacquelaine ;  Poggiale,  loc.  cit. ;  Benedict,  Proc.  Amer.  Acad.,  xxix,  212. 
tt  Benedict,  loc.  cit. 

§§  This  type  was  described  as  23  :  10 ;  see  Wells  and  Foote,  Amer.  Jour. 
Sci.,  iii,  461. 

II  ||  Herty,  loc.  cit. 


OTHER  DOUBLE  HALIDES  OF  ANTIMONY.        409 

caesium  double  fluorides  extend  farther  at  the  antimony  end 
than  the  others,  while  they  do  not  extend  as  far  at  the  alkali- 
metal  end  of  the  series  of  types. 

When  all  the  types  of  antimonious  double  halides  are  con- 
sidered, they  are  remarkable  for  their  large  number,  ten. 
This  number  is  probably  greater  than  is  the  case  with  any 
other  negative  element.  The  types,  1  :  3,  1 :  2,  4  :  7,  3  :  4, 
1:1,  3:2,  2:1,  7:3,  3:1,  and  4:1,  with  two  or  three 
exceptions,  are  the  simplest  that  can  exist  in  such  number 
between  the  two  extremes,  and  arithmetically  they  extend 
almost  as  far  in  one  direction  as  the  other. 

Method  of  Preparation.  —  Solutions  of  caesium  fluoride  and 
antimonious  fluoride  were  prepared  by  treating  caesium  car- 
bonate and  antimonious  oxide,  each  with  an  excess  of  pure 
hydrofluoric  acid.  To  the  antimonious  solution  the  caesium 
salt  was  gradually  added  in  small  quantities,  and  after  each 
addition  the  liquid  was  evaporated  and  cooled  until  crystalli- 
zation took  place.  If  a  homogeneous  product  was  obtained 
a  portion  was  removed  for  analysis,  and  the  process  was  con- 
tinued until  finally  the  liquid  contained  a  very  large  excess  of 
caesium  fluoride.  In  every  case  the  products  were  carefully 
inspected  to  make  sure  that  they  were  not  mixtures,  and  at 
least  two  crops  of  a  salt  were  always  prepared  under  some- 
what different  conditions,  and  were  shown  by  analysis  to  be 
identical  in  composition  before  they  were  accepted  as  true 
compounds. 

Method  of  Analysis.  —  The  crystals  were  carefully  dried  by 
pressing  between  filter  papers,  and  the  portions  to  be  analyzed 
were  preserved  in  glass  weighing-tubes  which  were  coated 
within  with  a  very  thin  layer  of  paraffine.  For  the  deter- 
mination of  antimony  and  caesium  a  portion  was  heated  in 
a  platinum  crucible  with  concentrated  sulphuric  acid  until 
all  the  hydrofluoric  acid  was  removed,  the  residue  was  dis- 
solved in  hydrochloric  acid,  antimony  was  precipitated  as 
sulphide,  collected  on  a  Gooch  crucible  and  weighed  after 
drying  in  a  small  oven  containing  carbon  dioxide.  Caesium 
was  weighed  as  normal  sulphate.  Fluorine  was  determined 


410         CJESIUM  ANTIMONIOUS  FLUORIDES  AND 

by  converting  it  into  silicon  fluoride,  collecting  the  latter 
in  water,  and  titrating  with  sodium  hydroxide,  according  to 
a  modification  of  Offermann's  method.  The  results  of  these 
fluorine  determinations  were  invariably  somewhat  too  low,  as 
we  found  by  testing  the  method  with  pure  potassium  silicon 
fluoride;  hence  the  chief  value  of  these  determinations  con- 
sist in  showing  that  the  salts  under  investigation  were  not 
oxy-compounds. 

1  :  2  Ccesium  Antimonious  Fluoride,  CsF.%SlFz.  —  This  salt 
was  obtained  in  the  form  of  beautiful  transparent  needles  by 
adding  2  or  3  g.  of  caesium  fluoride  to  a  solution  of  about  50  g. 
of  antimonious  fluoride  in  somewhat  dilute  hydrofluoric  acid 
solution,  heating  to  boiling  and  cooling.  Two  separate  crops 
gave  the  following  results  upon  analysis : 


Calculated  for 
CsSb2F7. 


Csesium 26.28  26.44 

Antimony  ....     47.43  47.36        47.42 

Fluorine      ....     26.28  25.23 

1  :  3  Ccesium  Antimonious  Fluoride,  CsF.3SbFs.  —  This 
salt  crystallizes  in  the  form  of  stout,  transparent  prisms. 
It  was  obtained  by  evaporating  the  mother-liquors  from  the 
preceding  compound  and  cooling,  or  by  the  use  of  somewhat 
less  caesium  fluoride  in  proportion  to  the  antimonious  fluoride 
in  a  more  concentrated  solution.  Two  crops  gave  the  follow- 
ing results : 

Calculated  for  Foun(L 

CsSb3P10.  r—[—  —^ 

Csesium 19.47  17.81        17.60 

Antimony  ....     52.71  52.95        53.89 

Fluorine      ....    27.82  27.01        26.84 

The  rather  wide  variation  of  the  results  from  the  calculated 
quantities  is  probably  due  to  the  fact  that  the  crystals  were 
taken  from  a  very  concentrated  antimonious  fluoride  solution 
and  were  consequently  not  quite  pure,  even  after  careful  dry- 
ing on  paper. 


OTHER  DOUBLE  HALIDES  OF  ANTIMONY.        411 


4  •  7  Ccesium  Antimonious  Fluoride,  4C8F>7iSbFa.  —  This 
salt  crystallizes  in  transparent  plates,  and  is  formed  in  the 
presence  of  a  little  larger  proportion  of  caesium  fluoride  than 
the  preceding  compounds.  It  was  obtained,  for  instance,  upon 
adding  about  4  g.  of  caesium  fluoride  to  a  mother-liquor  from 
the  last  salt  and  crystallizing  by  cooling.  Two  crops  gave  the 
following  results: 

Calculated  for  Found. 


Caesium 28.80  28.99 

Antimony   ....     45.47  46.02        46.03 

Fluorine      ....    25.73  24.58        24.61 

We  cannot  say  that  we  are  absolutely  sure  about  the 
formula  of  this  apparently  complicated  double  salt.  It  can- 
not be  a  1  :  2  compound,  for  not  only  is  it  entirely  distinct 
in  appearance  from  CsF.2SbF8,  but  coming  as  it  does  from  a 
strong  antimony  solution,  the  results  would  naturally  come 
too  high  rather  than  too  low  for  antimony.  The  results  vary 
too  widely  from  a  2  :  3  ratio  to  make  that  probable,  but  they 
approach  somewhat  more  closely  the  3  :  5  ratio.  The  follow- 
ing calculations  will  show  that  we  have  selected  the  most 
probable  formula: 

Calculated  for  Calculated  for          Calculated  for 

CB2SbsFu.  CsjSbgF^.  CsSb,F7. 

Cesium 31.86  29.75  26.28 

Antimony   ....     43.11  44.75  47.43 

Fluorine      ....    25.03  25.50  26.28 

1  : 1  Caesium  Antimonious  Fluoride,  CsF.SbF^.  —  In  the 
presence  of  still  greater  proportions  of  caesium  fluoride  this 
salt  is  produced  by  cooling  the  properly  concentrated  solution. 
It  forms  square  prisms,  the  ends  of  which  are  not  usually 
modified  by  any  planes.  Three  crops  gave  the  following 
analyses : 

Calculated  for  *^ 


Cs8bF4. 

Caesium   .     .     .     40.43  41~44  41.19 

Antimony    .     .     36.47  35.85  35.66        35.52 

Fluorine.  23.10  22.30  


412         CAESIUM  ANTIMONIOUS  FLUORIDES  AND 

2  :  1  Caesium  Antimonious  Fluoride,  %CsF.SbFs.  —  This 
salt  is  formed  under  a  wide  range  of  conditions  when  csesium 
fluoride  is  present  in  large  excess  hi  comparison  with  the  anti- 
monious fluorine.  It  crystallizes  in  apparently  rhombic  prisms, 
which  are  often  somewhat  flattened.  Four  crops,  made  under 
very  different  conditions,  gave  the  following  results : 

Calculated  for  Foun<L 


Cesium 

5530 

i. 

5481 

n. 

in. 

IV. 

Antimony 
Fluorine    . 

.     24.95 
.    19.75 

24.72 
19.42 

24.59 

24.92 

24.64 

By  the  use  of  very  concentrated  caesium  fluoride  solutions 
with  comparatively  small  amounts  of  antimonious  fluoride, 
no  evidence  was  obtained  of  the  existence  of  any  double 
salts  containing  more  csesium  fluoride  than  the  one  just 
described. 

Ccesium  Antimonious  Iodide,  3CsI.£SbIB.  —  It  appears 
that  no  compound  of  csesium  iodide  with  antimonious 
iodide  has  been  described.  The  sparingly  soluble  chloride, 
3CsC1.2SbCl8  is  well  known,  and  this  was  the  only  double 
chloride  that  Remsen  and  Saunders  *  were  able  to  prepare, 
although  four  rubidium  antimonious  chlorides  are  known. 
It  is  evident  that  the  slight  solubility  of  csesium  antimoni- 
ous chloride  makes  it  impossible  to  prepare  concentrated 
solutions  of  the  component  chlorides,  and  consequently  pre- 
vents the  formation  of  salts  of  other  types.  We  have  found 
that  an  iodide  which  corresponds  in  composition  to  the  chloride 
can  be  readily  prepared.  It  is  sparingly  soluble  in  hydriodic 
acid  solutions,  and  it  exists  in  two  distinct  forms,  one  of 
which  is  brick-red  and  apparently  octahedral  in  form,  while 
the  other  is  yellow  and  occurs  in  thin  hexagonal  plates.  The 
octahedral  salt  was  prepared  by  mixing  antimonious  iodide  and 
csesium  iodide  in  rather  strong  hydriodic  acid  solutions,  while 
the  yellow  hexagonal  salt  was  made  in  much  less  strongly  acid 
solutions,  particularly  upon  diluting  them  with  water,  boil- 

*  Loc.  cit 


OTHER  DOUBLE  HALIDES  OF  ANTIMONY.        413 

ing,  and  cooling.     Two  crops  of  each  form  were  analyzed  as 
follows  : 

Found. 


CasSbJa.                         Red  Salt. 

Yellow  Salt. 

i. 

n. 

I. 

n. 

Caesium     . 

.    22.39 

23.46 

.  .  . 

22.15 

... 

Antimony 

.    13.47 

13.91 

13.19 

14.36 

14.52 

Iodine  .     . 

.    64.14 

62.98 

.  .  . 

63.03 

.  .  . 

This  was  the  only  double  iodide  that  we  were  able  to  obtain. 

There  is  little  doubt  that  a  corresponding  bromide  exists, 
for  we  observed,  while  engaged  in  work  with  another  object  in 
view,  that  a  yellow  precipitate  is  produced  when  the  bromides 
of  caesium  and  trivalent  antimony  are  brought  together  in 
solution.  Having  overlooked  the  fact  that  thejcompound  had 
not  been  described,  we  neglected  to  analyze  the  product. 

Ccesium  Antimonic  Halides.  —  So  little  is  known  concerning 
the  double  halides  of  quinquivalent  elements  that  it  seemed 
desirable  to  study  the  caesium  antimonic  compounds.  Setter- 
berg  *  has  described  a  single  double  chloride,  CsCl.Sb.Cl5,  and 
we  have  confirmed  his  result,  but  by  using  widely  varying 
conditions  we  have  been  unable  to  prepare  any  other  compound. 
Setterberg's  salt  crystallizes  in  long,  colorless,  transparent 
needles.  A  crop  of  it  gave  the  following  results  upon  analysis  : 

Calculated  for 


Osium   .....    28.54  29.14 

Antimony    ....     25.75  26.43 

Chlorine       ....    45.70  43.94 

We  have  extended  our  investigation  to  antimonic  fluoride 
and  caesium  fluoride,  but  the  results  were  disappointing  from  the 
the  fact  that  we  were  able  to  prepare  but  one  double  salt,  while 
Marignacf  has  described  two  potassium  antimonic  fluorides. 
Either  caesium  in  this  case  unexpectedly  fails  to  show  as 
great  a  tendency  to  form  double  salts  as  does  potassium,  or 
else  we  have  failed  to  find  the  proper  conditions  for  produc- 
ing them. 

*  Loc.  cit.  t  Liebig's  Ann.,  cxlv,  237. 


414  CESIUM  ANTIMONIOUS  FLUORIDES. 

The  salt  obtained  by  us  apparently  contains  hydroxyl, 
although  prepared  in  strong  hydrofluoric  acid  solutions,  and 
has  the  formula  CsF.SbF4OH.  It  crystallizes  on  cooling 
warm,  rather  concentrated  solutions  in  the  form  of  bundles  of 
transparent  needles.  Two  crops  gave  the  following  analyses : 

Calculated  for  Fou.D(L 

CsSbF5OH.  T~  ~~n — ' 

Caesium 36.44  37.77 

Antimony  ....  32.87  31.82        31.72 

Fluorine     ....  26.03  25.54        26.18 

Hydroxyl   ....  4.66  (4.87) 

LD  SCIENTIFIC  SCHOOL, 
April,  1901. 


ON  THE  DOUBLE  CHLORIDES   OF  (LESIUM 
AND   THORIUM. 

BY  H.  L.  WELLS  AND  J.  M.  WILLIS. 

NEAKLY  all  of  the  known  double  halogen  salts  of  quadri- 
valent metals  belong  to  a  single  type,  of  which  2KCl.PtCl4 
and  2KF.SiF4  are  examples.  It  has  been  shown,  however, 
by  Marignac*  and  by  Wells  and  Foote  f  that  the  double  flu- 
orides of  zirconium  exist  in  a  variety  of  types.  Therefore, 
since  thorium  is  somewhat  closely  related  to  zirconium,  we 
have  undertaken  an  investigation  of  some  thorium  double 
halides,  and  have  selected  the  caesium  salts  as  being  the  most 
promising. 

Upon  attempting  to  prepare  caesium  thorium  fluorides  we 
found  that  thorium  fluoride  is  practically  insoluble  even  in 
concentrated  solutions  of  caesium  fluoride  containing  hydro- 
fluoric acid.  There  is  no  doubt  that  the  two  fluorides  combine 
under  these  circumstances,  but,  since  we  obtained  only  finely 
divided  precipitates  as  products  and  there  was  no  certainty  as 
to  their  purity,  further  work  on  the  fluorides  was  abandoned. 
Chydenius  $  has  previously  described  two  potassium  thorium 
fluorides,  2KF.ThF4.4H2O  and  KF.ThF4.JH2O,  but  on  account 
of  the  insolubility  of  thorium  fluoride  and  of  these  double  salts 
it  is  probable  that  there  may  be  some  doubt  in  regard  to  the 
correctness  of  these  formulas. 

We  have  prepared  two  caesium  thorium  chlorides,  to  which 
we  assign  the  formulas  3CsCl.ThCl4.12H2O  and  2CsCl.ThCl4. 
11H2O.  The  amount  of  water  of  crystallization  in  these  com- 
pounds is  somewhat  uncertain,  since  they  form  very  small 
hygroscopic  crystals,  and  it  is  difficult  to  dry  them  by  pressing 

*  Amer.  Chim.  Phys.,  Ill,  lx,  257. 
t  Amer.  Jour.  Sci.,  IV,  i,  18;  iii,  466. 
t  Pogg.  Ann.,  cxix,  43. 


416  THE  DOUBLE   CHLORIDES 

on  paper.  The  search  for  double  chlorides  was  made  system- 
atically by  starting  with  a  solution  of  about  65  g.  of  thorium 
chloride  in  hydrochloric  acid,  adding  2  to  4  g.  of  csesium 
chloride  at  a  time,  and  evaporating  and  cooling  after  each 
addition,  until  finally,  after  dividing  the  solution  and  using  a 
part  of  it,  a  very  large  excess  of  csesium  chloride  was  present. 

In  analyzing  the  salts  chlorine  was  determined  as  silver 
chloride,  sometimes  in  separate  portions,  in  other  cases  in  the 
nitrates  from  which  thorium  hydroxide  had  been  precipitated ; 
thorium  was  weighed  as  oxide  after  precipitation  with  ammonia, 
and  the  csesium  in  the  filtrates  was  converted  into  normal 
sulphate  and  weighed  as  such;  water  was  determined  by 
difference. 

3 : 1  Ccesium  Thorium  Chloride,  3  Os  01.  Th  Oli.WH*  0.  —  This 
salt  was  produced  from  solutions  containing  about  12  g.  of 
thorium  chloride  and  from  30  to  110  g.  of  csesium  chloride. 
It  forms  colorless  crystals  of  feathery  structure  upon  cooling 
very  concentrated  solutions.  Three  different  crops  made 
under  somewhat  varied  conditions  gave  the  following  results 
upon  analyses : 

Caesium  .     . 
Thorium 
Chlorine 
Water    .    . 

2:1  Ocesium  Thorium  Chloride,  20sOl.ThCl^llH20.  - 
This  salt  was  obtained  in  colorless  crystals,  somewhat  resem- 
bling the  previous  salt,  but  not  nearly  as  feathery  in  appearance. 
It  was  formed  in  concentrated  solutions  containing  about  65  g. 
of  thorium  chloride  and  from  30  to  100  g.  of  csesium  chloride. 
The  following  analyses  were  made  of  different  crops : 


Calculated  for 
Cs3ThCl7.12H2O. 

.     36.45 

f  ounu. 

r    i. 
36.21 

II. 

36.14 

in. 

.     21.20 

20.70 

21.68 

21.05 

.     22.61 

23.09 

.  .  . 

23.37 

.     19.74 

(20.00) 

.  .  . 

.  .  . 

Caesium    . 

Calculated  for 
Cs2ThCl6.llH20. 

.     29.26 

JTOU 

na. 

i. 

29.84 

II. 

29.10 

III. 

28.92 

IV. 

Thorium  . 

.    25.52 

25.42 

25.41 

25.70 

25.22 

Chlorine  . 

.    23.43 

23.40 

24.75 

23.35 

23.55 

Water      . 

.     21.78 

(21.34) 

(20.74) 

(22.03) 

.  .  . 

OF  CAESIUM  AND  THORIUM.  417 

The  salt  loses  water  slowly  in  the  desiccator  over  sulphuric 
acid.  A  sample  dried  in  this  way  lost  six  per  cent  in  two  days, 
eleven  per  cent  after  one  week,  and  twenty  per  cent,  corre- 
sponding to  practically  all  the  water,  after  one  month. 

The  two  chlorides  that  we  have  obtained  are  different  in 
type  from  the  potassium  salt  KC1.2ThCl4.18HaO  described  by 
Cleve,*  and  from  the  ammonium  salt  8NH4Cl.ThCl4.8H2O 
described  by  Chydenius. f  It  seems  certain  that  the  ammonium 
salt  just  mentioned  represents  a  mixture  for  it  is  described  as 
a  sintered  mass  made  in  the  dry  way. 

*  Bulletin,  xxi,  118.  t  Fogg.  Ann.,  cxix,  43. 


27 


ON  A  CAESIUM  TELLURIUM  FLUORIDE. 

BY  H.  L.  WELLS  AND  J.  M.  WILLIS. 

SEVERAL  tellurium  double  fluorides  have  been  described: 
NaF.TeF4  by  Berzelius,  KF.TeF4,  NH4F.TeF4,  and  BaF2. 
2TeF4.H2O  by  Hogbom.*  It  is  noticeable  that  all  these 
fluorides  belong  to  a  type  which  is  different  from  that  of  the 
double  chlorides,  bromides,  and  iodides  of  tellurium,  e.  g.,  2KC1. 
TeCl4,  2RbBr.TeBr4,  and  2CsI.TeI4,  etc.,  which  have  been 
thoroughly  studied  in  this  laboratory  by  Wheeler,  f  We  have 
undertaken,  therefore,  an  investigation  of  the  combination  of 
caesium  fluoride  with  tellurium  fluoride,  with  the  expectation 
that  possibly  several  types  of  double  fluorides  might  be  ob- 
tained. After  a  systematic  examination  of  the  matter,  how- 
ever, we  were  able  to  prepare  only  one  double  fluoride, 
CsF.TeF4,  which  corresponds  in  type  to  the  previously  known 
fluorides. 

A  concentrated  solution  of  TeF4  was  prepared  by  dissolving 
about  10  g.  of  pure  TeO2  in  an  excess  of  strong  hot  hydro- 
fluoric acid,  and  to  this  caesium  fluoride  was  added  in  small 
portions,  the  liquid  being  concentrated  by  evaporation  and 
cooled  after  each  addition.  At  the  same  time  small  portions 
of  tellurium  fluoride  were  added  to  a  concentrated  solution  of 
about  50  g.  of  caesium  fluoride  in  hydrofluoric  acid,  and  this 
solution  was  evaporated  and  cooled  in  the  same  manner. 
Under  the  widest  range  of  conditions,  however,  only  a  single 
double  salt  was  obtained. 

1:1  Ccesium  Tellurium  Fluoride,  CsF.TeF4. — This  salt 
crystallizes  beautifully  in  large,  transparent,  colorless  needles. 
The  presence  of  free  hydrofluoric  acid  is  necessary  for  its 
formation,  for  it  is  decomposed  by  water.  Several  crops, 

*  Bulletin,  xxv,  60.  t  Amer.  Jour.  Sci.,  Ill,  xlv,  267. 


ON  A    CAESIUM  TELLURIUM  FLUORIDE.  419 

made  under  widely  varying  conditions,  were  analyzed  with 
the  following  results  : 


Calculated  for 


CsTeF8. 

i. 

n. 

IIL 

IV. 

Caesium 

.    37.36 

36.59 

37.50 

38.56 

37.23 

Tellurium  . 

.     35.96 

35.51 

36.45 

35.82 

35.60 

Fluorine 

.    26.68 

26.76 

24.51 

26.18 

•  •  • 

Fluorine  was  determined  volumetrically  by  converting  it 
into  SiF4,  collecting  this  in  water,  and  titrating  with  a  standard 
solution  of  potassium  hydroxide.  In  another  portion,  after 
evaporating  with  concentrated  sulphuric  acid,  and  dissolving 
the  residue  in  hydrochloric  acid,  tellurium  was  precipitated  with 
sulphur  dioxide,  collected  on  a  Gooch  crucible,  and  weighed  as 
metal.  From  the  filtrate  from  the  tellurium  caesium  was  ob- 
tained, and  weighed  as  normal  sulphate. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
May,  1901. 


GENERALIZATIONS  ON  DOUBLE  HALOGEN  SALTS. 

BY  H.  L.  WELLS. 

THE  object  of  this  communication  is  to  point  out  some  con- 
clusions in  regard  to  double  halides  in  general  For  this  pur- 
pose a  rather  full  list  of  these  compounds  has  been  prepared. 
This  list  is  not  supposed  to  be  complete,  for  the  literature  has 
not  been  searched  with  care  except  in  the  cases  of  certain  series 
which  have  been  studied  in  the  laboratory,*  but  it  is  believed 
to  be  sufficiently  complete  for  the  purpose  in  view.  Care  has 
been  taken  to  consult  the  original  articles  where  salts  of 
unusual  composition  have  been  described,  and  a  few  of  these 
have  been  discarded  on  account  of  evidence  that  they  were  not 
real  compounds,  but  no  double  salt  has  been  rejected  simply 
because  it  appeared  to  be  irregular. 

It  has  been  thought  best  to  limit  the  present  discussion  to 
the  salts  of  the  alkali  metals,  ammonium,  and  univalent 
thallium;  for  to  include  the  double  halides  of  the  organic 
bases  and  those  in  which  bivalent  metals  form  the  more  posi- 
tive halides  would  greatly  enlarge  the  list,  probably  without 
giving  any  additional  insight  into  the  nature  of  the  compounds. 

For  the  sake  of  convenience  the  double  salts  will  be  arranged 
according  to  types,  which  will  be  designated  by  ratios  indicat- 
ing the  number  of  atoms  of  the  two  metals ;  thus,  KCl.SnCl4 
is  a  1  :  1  salt;  2KCl.PtCl4  is  a  2:1  salt;  and  CsC1.2PbCla 
is  a  1 :  2  salt.  The  number  referring  to  the  atoms  of  alkali 
metal,  etc.,  will  be  invariably  placed  first. 

*  See  Amer.  Jour.  Sci.  from  1892  to  the  present  time.  References  are 
given  beyond  to  most  of  these  articles,  but  reference  to  general  literature  is 
not  attempted. 


DOUBLE  HALOGEN  SALTS.  421 

I.  SALTS  OP  UNIVALENT  NEGATIVE  METALS. 

Cuprous  Salts.* 

3:1  2:1  3:2  1:1 

3CsCl.CuCl.H20     2NH4Cl.CuCl     3CsC1.2CuCl     NH4Cl.CuCl 
2NH4Br.CuBr  NH4Br.CuBr 

2KCl.CuCl  NH4I.CuI.H20 

2:3  1:2 

2NH4C1.3CuCl        CsCUCuCl 

Silver  and  Aurous  Salts.] 

2:1  1:1 

2KI.AgI  NH4Cl.AgCl 

2KbI.AgI  KCl.AgCl 

2CsCl.AgCl        KI.Agl 

KCLAuCl 

II.  SALTS  OF  BIVALENT  NEGATIVE  METALS. 

Beryllium  Salts. 

2:1  1:1 

2KF.BeF2  KF.BeF2 

2KCl.BeCl2 

Magnesium  Salts.]. 

1  :1 

NH4Cl.MgCl2.6H20  KCl.MgCl2.6H20 

NH4Br.MgBr2.6H2O  KBr.MgBr2.6H20 

NH4I.MgI2.6H20  KI.MgI2.6H20 

NaF.MgF2  EbCl.MgCl2.6H20 

NaCl.MgCl2.H20  CsC[MgClz.QHfl 

CsBr.MgBr2.6H20 

*  See  Amer.  Jour.  Sci.,  HI,  xlvii,  96. 

t  See  Ibid.,  xliv,  155. 

t  See  Wells  and  Campbell,  Ibid.,  Ill,  xlvi,  431. 


422 


GENERALIZATIONS  ON 


Manganese  Salts.* 


2:1 

2NH4Cl.MnCl2.2H20 
2EbCl.MnCl2.2H2O 
2CsCl.MnCl2.2H20 


1:1 

NH4Cl.MnCl2.2H2O 
KCl.MnCl2.2H20 
CsCl.MnCl2.2H2O 


Ferrous  and  Nickel  Salts. 


2:1 

2NH4Cl.FeCl2 

2KF.FeF2 

2KCl.FeCl2.2H20 

2NH4F.MF2.2H20 

2KF.NiF2 


1:1 

KF.FeF2.H20 

NH4Cl.NiCl2.6H2O 

NaF.NiF2.H20 

KF.NiF2.H20 

CsCl.NiCl2 

CsBr.NiBr2 


3:1 

3CsCl.CoCl2 
3CsBr.CoBra 


Cobalt 


2:1 

2NH4F.CoF2.2H20 

2CsCl.CoCl2 

2CsBr.CoBr2 

2CsI.CoI2 


1:1 

NH4Cl.CoCl2.6H20 
NaF.CoF2.H20 
KF.CoF2.H20 
CsCl.CoCl2.2H20 


2:1 

2NH4F.CuF2.2H2O 
2NH4Cl.CuCl2.2H20 
2NH4Br.CuBr2.2H2O 
2KF.CuF2 
2KCl.CuCl2 
2CsCl.CuCl2 
2CsCl.CuCl2.2H2O 
2CsBr.CuBr2 


Oupric  Salts.  J 

3:2 

3CsC1.2CuCl2.2H20 


1:1 

NH4F.CuF2.2£H20 

NH4Cl.CuCl2.2H20 

LiCl.CuCl2.2H2O 

KF.CuF2 

EbF.CuF2 

CsCl.CuCl2 

CsBr.CuBr2 


*  See  Saunders,  Amer.  Chem.  Jour.,  xiv,  152. 
t  See  Campbell,  Amer.  Jour.  Sci,,  III,  xlviii,  418. 
t  See  Wells  and  Dupee,  Ibid.,  Ill,  xlvii,  91. 


DOUBLE  HALOGEN  SALTS. 


423 


4:1 
4NH4Cl.ZnCl2 

1:1 

NH4Cl.ZnCl2.2H2O 

NaF.ZnF, 

NaI.ZnI2.3H20 

KF.ZnF2 

KI.ZnL, 


Zinc  Salts* 

3:1 
3NH4Cl.ZnCl2 

3CsCLZnCl2 

3CsBr.ZnBr2 

3CsI.ZnI2 


2:1 

2NH4F.ZnF2.2H20 
2NH4Cl.ZnCl2 
2NH4Cl.ZnCl2.H20 
2NH4Br.ZnBr2 
2KE4I.ZnI2 
2NaCl.ZnCl2.3H20 
2NaI.ZnI2.3H20 
2KF.ZnF2 
2KCl.ZnCl2 
2KI.ZnI3 
2CsCl.ZnCl2 
2CsBr.ZnBra 
2CsI.ZnI2 


4:1 

4NH4Cl.CdCla 
4NH4Br.CdBr2 
4KCl.CdCl2 
4KBr.CdBr2 

1:1 

NH4F.CdF2 

NH4Br.CdBr24H20 

JSTaBr.CdBr2.2^H20 

KCl.CdCl, 

KCl.CdCl2.iH20 

KBr.CdBr24H20 

KI.CdI2.H20 

CsCl.CdCl, 

CsBr.CdBra 

CsI.CdI2 


Cadmium 


3:1 

3CsBr.CdBra 
3CsI.CdI2 


2:1 

2NH4Cl.CdCl2 
2NH4Cl.CdCl2.H20 


2NH4I.CdI2.2H20 

2NaCl.CdCl2.3H20 

2NaBr.CdBr2.5H20 

2NaI.CdI2.6H20 

2KCl.CdCl2 

2KCl.CdCl2.H20 

2KBr.CdBr2 

2KI.CdI2.2H20 

2CsCl.CdCl2 

2CsBr.CdBr2 

2CsI.CdI2 


*  See  Wells  and  Campbell,  Amer.  Jour.  Sci.,  IH,  xlvi,  431. 
t  See  Wells  and  Walden,  Ibid.,  425. 


424 


GENERALIZATIONS  ON 


4:1 
4NH4Cl.SnCl2.3H20 


2:3 

2NaF.3SnF2 
2KF.3SnF2.H20 


Stannous  Salts. 

2:1 

2NH4F.SnF2.2H20 
2XH4Cl.SnCl2.H20 


1:1 

NH4I.SnI2 
NH4I.SnI2.lpI20 
NaLSnl, 


3:1 

3CsCl.HgCl2 
3CsBr.HgBr2 
3CsI.HgI2 


Mercuric  Salts.' 

2:1 

2NH4Cl.HgCl2.H20 

2NH4Br.HgBr2 

2NH4I.HgI2.3H20 

2NaCl.HgCl2 

2NaI.HgI2 

2KCl.HgCl2.H20 

2KBr.HgBr2 

2KI.HgI2 

2EbCl.HgCl2 

2KbCl.HgCl2.2H20 

2CsCl.HgCl2 

2CsBr.HgBr2 

2CsI.HgI2 


2:3 

2NH4C1.3HgCl2.4H20 
2CsI.3HgI2 


1:2 

KC1.2HgCl2.2H20 

KbC1.2HgCl2 

CsC1.2HgCl2 

CsBr.2HgBr2 

CsI.2HgI2 


NH4Cl.HgCl2 

NH4Cl.HgCl2.H20 

NH4Br.HgBr2 

NH4I.HgI2.H20 

LiCl.HgCl2 

NaCl.HgCl2.l£H20 

NaBr.HgBr, 


KCl.HgCl2 

KCl.HgCl2.H20 

KBr.HgBr, 

KBr.HgBr2.H20 

KI.HgI2.liH20 

KbCl.HgCl, 

CsCl.HgCl2 

CsBr.HgBr2 

CsLHgI2 

TlCl.HgCl2 

1:6 

NH4C1.5HgCl2 
CsC1.5HgCl2 


*  See  Amer.  Jour.  Sci.,  Ill,  xliv,  221. 


DOUBLE  HALOGEN  SALTS. 


425 


Palladious,  Platinous,  and  Iridious  Salts. 


2:1 


2NH4Cl.PdCl2 

2NH4Cl.PtCl2 

2NHJ.IrI2 

2£TaCl.PdCl2 

2NaCl.PtCl2.4H20 


4:1 

4CsCl.PbClf 
4CsBr.PbBr2 

1:2 

NH4C1.2PbCl2 
NH4Br.2PbBr2 
KC1.2PbCl2 
KBr.2PbBr2 
KbC1.2PbCl2 
B,bBr.2PbBr2 
CsC1.2PbCl2 
CsBr.2PbBr2 


2KCl.PdCl2 
2KCl.PtCl2 
2KBr.PtBr2 
2CsCl.PdCl2 
2CsCl.PtCl2 

Lead  Salts* 

2:1 

2NH4Br.PbBr2.H20 
2KBr.PbBr2.H20 
2RbCl.PbCl2.£H20 
2KbBr.PbBr24H20 


1:1 

LiCl.PtCl2.6H20 
KCl.PdCl2 
KCl.PtCl2 
KbCl.PtCl2 


1:1 

NH4Cl.PbCl24H20 

NH4I.PbI2.2H20 

KCl.PbCl2.£H20 

KBr.PbBr24H20 

KBr.PbBr2.H20 

KI.PbI2.2H20 

EbI.PbI2.2H2O 

CsCl.PbCl2 

CsBr.PbBr2 

CsI.PbI2 


III.  SALTS  OP  TRWALENT  NEGATIVE  METALS. 


Aluminum  Salts. 


3:1 


3KaF.AlF8 
3KF.A1F8 


2:1 

2NaF.AlF8 
2KF.A1F8 


3:2 

3NaF.2AlF8f 


3:1 

3NH4F.VF8 

1:1 

NH4F.VF8.2H20 


Vanadium  Salts. 

5:2 

5NaF.2VF8.H20 


1:1 

NaCl.AlCl8 
KC1.A1C18 
KBr.AlBr, 
KI.A1I8 


2:1 

2NH4F.VF8.H20 
2KF.VF8.H20 


*  Nearly  all  the  older  work  on  double  halides  of  lead  was  entirely  erro- 
neous. See  Remsen  and  Herty,  Amer.  Chem.  Jour.,  xiv,  107 ;  Wells,  Amer. 
Jour.  Sci.,  Ill,  xlr,  121 ;  Wells  and  Johnson,  Ibid.,  xlvi,  25,  34. 

t  The  formula  for  chiolite  is  somewhat  doubtful.  Some  authorities  prefer 
the  formula  6NaF.3AlF8,  but  the  simpler  formula  is  selected  here. 


426  GENERALIZATIONS  ON 

Chromium  Salts.* 

3:1  2:1  1:1 

3NH4F.CrF8  2NH4F.CrF8.H20  KCl.CrCl8 

3KF.CrF8  2NH4Cl.CrCl3.H20 

3KCl.CrCl8  2NaF.CrF8.H20 

3TlCl.CrCl8  2KF.  CrF3.H2O 

2KCl.CrCl3.2H20 

2CsCl.CrCl3.H20 

2CsCl.CrCl8.4H20 

Titanous  and  Manganic  Salts. 

3:1  2:1 

3NH4F.TiF8  2NH4F.  MnF8 

2NaF.MnF8 
2KF.MnF8 
2NH4F.TiF8 

Ferric  SaltsJ 

3:1  2:1  1:1 

3NH4F.FeF8  2NH4F.FeF3  NH4Br.FeBr8.2H20 

3KF.FeF8  2NH4Cl.FeCl8          CsCl.FeCls 

3CsCl.FeCl8.H20      2NaF.FeF8.|H20      CsBr.FeBra 
3TlCl.FeCl8  2NaCl.FeCl8.H20 

2KF.FeF8 

2KCl.FeCl8.H20 

2BbCl.FeCl3H20 

2EbBr.FeBrs.H20 

2CsCl.FeCl8.H20 

2CsBr.FeBr8.H2O 

Arsenious  Salts.$ 

3:2 

3EbC1.2AsCl8  3CsC1.2AsCl8 

3EbBr.2AsBr8  3CsBr.2AsBr3 

3RbI.2AsI8  3CsI.2AsI8 

*  See  Wells  and  Boltwood,  Amer.  Jour.  Sci.,  III,  i,  249. 
t  See  Walden,  Ibid.,  Ill,  xlviii,  283. 
J  Wheeler,  Ibid.,  Ill,  xlvi,  88. 


DOUBLE  HALOGEN  SALTS. 


427 


Indium  Salts. 


8:1 

3KCl.InCl8.lpI20 


2:1 
2NH4Cl.InCl8.H20 


4:1 
4NH4I.SbI8.3H2O 


2:1 

2NH4F.SbF8 

2NH4Cl.SbCl8 

2NH4Cl.SbCl8.H2O 

2LiF.SbF8 

2KF.SbF3 

2KCl.SbCl8 

2KCl.SbCl8.2H20 

2CsF.SbF8 


Antimonious  Salts. 

3:1 

3NH4Cl.SbCl8.liH2O 
3NaF.SbF8 

SNaCLSbCL 


3:2 

3NH4L2SbI8.3H20 

3NaI.2SbI8.12H20 

3KI.SbI8.3H20 

3EbC1.2SbCl8 

3EbBr.2SbBr8 

3RbI.2SbI8 

3CsC1.2SbCl8 

3CsI.2SbI« 


3:4  4:7 

3NH4I.4SbI8.9H20    4CsF.7SbF8 

1:3 

CsF.3SbF8 


7:3 

7KC1.3SbCl8 
7KBr.3SbBr8.8H20 
7RbC1.3SbCl8 
7EbBr.3SbBr8 

1:1 

NH4Cl.SbCl3 
NH4I.SbI8.2H2O 
KF.SbF8 
KI.SbI8.H20 

EbCl.SbCl8 
CsF.SbF8 


1:2 

EbC1.2SbCl8 
CsF.2SbF8 


Auric  Salts,  f 

1:1 

NH4Cl.AuCl8.H20 


NaCl.AuCl8.2H2O 

NaBr.AuBr8.2H2O 

KCl.AuCl84H20 

KCl.AuCl8.2H2O 

KBr.Aubr8.2H2O 


KIAuI8 

EbCl.AuCl, 

RbBr.AuCl8 

CsCl.AuCl8 

CsCl.AuCl84H2O 

CsBr.AuBr8 

TlCl.AuCl8 


*  See  Wheeler,  Amer.  Jour.  ScL,  in,  Ixvi,  269;  Wells  and  Metzger,  Ibid., 
June,  1901. 

t  See  Wells  and  Wheeler,  Ibid.,  HI,  xliv,  157. 


428 


GENERALIZATIONS  ON 


4:1 

4NH4Cl.BiCl8 
4KI.BiI8 


2:1 

2NH4Cl.BiCl8 
2NaCl.BiCl8.3H20 
2KCl.BiCl3.2H20 
2KI.BiI8.H2O 

1:2 

NH4C1.2BiCl8. 


Bismuth  Salts. 

3:1 

3NH4Cl.BiCl8 

3NaCl.BiCl8 

3KCl.BiCl8 

3KI.BiCl8 

3EbCl.BiCl8 

3CsCl.Bi018 

3:2 

3NaI.2BiI8 
3KC1.2BiCl8 
3CsC1.2BiCl8 


7-3 
7EbC1.3BiCl8 


NH4Cl.BiCl8 
KCl.BiCl8.H20 
KI.BiI8 
KbCl.BiCl8.H20 


5:1 
5T1I.T1I8 

3:2 

3KC1.2T1C18.1£H20 
3LBr.2TlBr8.3H20 
3KI.2T1I8.3H20 
3CsC1.2T1018 
3CsBr.2TlBr8 


Thallic  Salts* 

3:1 

3NH4C1.T1C18.2H2O. 
3NH4C1.T1C18 
3NH4I.T1I8 
3LiCl.TlCl8.8H20 
3NaCl.TlCl8.12H20 
3KC1.T1C1S.2H20 
3KbCl.T1018.H20 
3EbBr.TlBr8.H20 
3CsCl.TlCl8.H20 
3T1C1.T1C18 
3TlBr.TlBr8 


2:1 

2KC1.T1C18.2H20 
2EbCl.TlCl8.H20 
2CsCl.TlCl8 
2CsCl.TlCl8.H20 

1:1 

NH4Br.TlBr8.2H20 
NH4Br.TlBr8.4H20 
NH4Br.TlBr8 
NH4I.T1I8 
KBr.TlBr, 

KI.TlIg 

EbBr.TlBr8 

EbI.TlI3 

CsBr.TlBr8 

CsI.TlI8 

T1C1.T1C18 

TlBr.TlBr8 


*  See  Pratt,  Amer.  Jour.  Sci.,  Ill,  xlix,  397. 


DOUBLE  HALOGEN  SALTS. 


429 


Rhodium,  Ruthenium,  Iridium,  and  Osmium  Salts. 


3:1 

3NH4Cl.RhCl8.HH20  3NaBr.IrBr84H2O 
3NH4Cl.IrCl3.liH20    3KCl.EhCl8 
3NH4Br.IrBr84H20    3KCUrCl8.3H20 
3NH4I.IrI84H20         3KBr.IrBr8.3H20 
3NaCl.RhCl8.9H20      SKLIrl, 
3NaCl.IrCl8.12H20      3KC1.0sCl3.6H20 


2:1 

2NH4Cl.KliCl8.H20 
2NH4Cl.RuCl8 
2NH4Cl.OsCl8.liH20 
2KCl.KhCl8.H20 
2KCl.EhCl8.3H20 
2KCl.R,uCl8 


IV.  SALTS  OF  QUADKIVALENT  NEGATIVE  METALS. 
Titanic,*  Germanium,  and  Manganese  Salts. 

2:1 

2NH4F.TiF4  2KbF.TiF4 

2NaF.TiF4  2KF.MnF4 

2KF.TiF4.H20  2KF.GeF4 


4:1 

4LiF.ZrF4.§H20 


6:3 
5TlF.3ZrF4 


Zirconium  Salts,  f 


3:1 

3NH4F.ZrF4 
3KF.ZrF4 


5:2 
5NaF.2ZrF4 


1:1 

KF.ZrF4.H20 
CsF.ZrF4 
TlF.ZrF4 
TlF.ZrF4.H20 


2:1 

2NH4F.ZrF4 
2LiF.ZrF4 
2NaF.ZrF4 

2NaGl.ZrGl4 

2KF.ZrF4 
2CsF.ZrF4 

2:3 
2CsF.3ZrF4.2H20 


*  Rose's  compounds,  6NH4Cl.TiCl4  and  3NH4Cl.TiCl4  are  omitted  here 
because  they  represent  sublimates  of  variable  composition.  Pennington's 
salt  4CsF.TtF4  is  also  left  out,  as  it  was  described  with  two  other  caesium 
salts  of  very  suspicious  composition  which  are  referred  to  under  the  pen- 
tivalent  compounds. 

t  See  Wells  and  Foote,  Amer.  Jour.  ScL,  IV,  i,  18;  iii,  466. 


430 


GENERALIZATIONS  ON 


Stannic  and  Antimony  Salts. 

4:1  2:1 

4NH4F.SnF4  2NH4Cl.SnCl4  2KF.SnF4.H20 

2LiF.SnF4.2H2O  2KCl.Sn014 

2NaF.SnF4  2KbCl.SnCl4 

2NaCl.SnCl4  2CsCl.SnCl4 

2NaCl.SnCl4.6HaO  2CsCl.SbCl4 
23TaBr.SnBr4.6H20 


2KCl.TeCl4 

2KBr.TeBr4.2H20 

2KI.TeI4.2H20 

2RbCl.TeCl4 

2EbBr.TeBr4 


Tellurium  Salts.* 

2EbI.TeI4 
2CsCl.TeCl4 
2CsBr.TeBr4 
2CsI.TeI4 

Ceric  Salt. 

3:2 

3KF.CeF4.2H20 


NH4F.TeF4 

KF.TeF4 

CsF.TeF4 


2NH4Cl.PdCl4 

2NH4Cl.RuCl4 

2NH4Cl.IrCl4 

2NH4Cl.Pt014 

2KH4C1.0sCl4 

2NH4Br.PtBr4 

2NH4Br.IrBr4 

2NH4I.PtI4 

2LiCl.PtCl4.6H20 

2NaCl.PtCl4.6H20 


Platinum  Group  Salts. 

2:  1 

2NaCl.IrCl4.6H80 

2NaC1.0sCl4 

2NaBr.IrBr4 

2NaI.PtI4.6H20 

2NaI.IrI4 

2KCl.PdCl4 

2KCl.KuCl4 

2KCl.PtCl4 

2KCl.IrCl4 


2KC1.0sCl4 

2KBr.PdBr4 

2KBr.PtBr4 

2KBr.IrBr4 

2KI.PtI4 

2KLM4 

2EbCl.PtCl4 

2CsCl.PtCl4 

2TlCl.PtCl4 


See  Wheeler,  Amer.  Jour.  Sci.,  in,  xlv,  267. 


DOUBLE  HALOGEN  SALTS.  431 


Plumbic  Salts* 

2:1 

2NH4Cl.PbCl4  2RbCl.Pb014 

2KCl.PbCl4  2CsCl.Pb014 


Thorium  Salts,  f 

3:1  2:1 

3CsCl.ThCl4.12H20  2KF.ThF4.4H20 

2CsCl.ThCl4.llH2O 

1:1  1:2 

KF.ThF44H20  KC1.2TliCl4.18H20 


V.  SALTS  OF  QUINQUIVALENT  NEGATIVE  METALS.J 

4:1  2:1  1:1 

4NH4Cl.SbCl6  2KF.AsF5  KF.AsF6 

2NH4F.SbF6  NH4F.SbF6 

2KF.SbF5  NaF.SbF5 

2KF.NbF6  KF.SbF6 

2EbF.NbF6 
2NH4F.TaF6 
2NaF.TaF6 
2KF.TaF6 
2EbF.TaF6 

*  See  Amer.  Jour.  ScL,  III,  xlvi,  180. 

t  The  salt  SNH^CLThCl^SHaO,  described  by  Chydenius  as  a  sintered 
mass  is  rejected,  as  is  also  8KF.7ThF4.6H2O,  which  Chydenius  himself  con- 
sidered to  be  probably  a  mixture. 

t  Pennington's  salts,  7CsF.NbF5  and  16CsF.TaF6  are  omitted  because  they 
differ  entirely  from  two  rubidium  salts  obtained  in  the  same  investigation 
(which  are  given  in  the  list),  and  because  they  depend  upon  single  partial 
analyses.  (See  Jour.  Amer.  Chem.  Soc.,  xviii,  69.)  It  is  impossible  to 
believe  that  caesium  and  rubidium  salts  of  the  same  metals  should  differ  so 
widely  as  they  appear  to  do. 


432 


GENERALIZATIONS  ON 


10 


..<N 

|          :       - 

rj  CO  •  *  CO 


4 


*•§ 


3       ••» 

r-\ 
t- 


ft 
02 


CO  CO 


CO 


(M 


CO 
<M 


CO 


CO 


I 

I 


-2 


O 

I 


1 

02 


CO 


CO 


CO 


co"     co 


CO 
XO 


CO  CO 


CO 


CO 


1O 


CO  CO 


CO 


10 


DOUBLE  HALOGEN  SALTS.  433 

Upon  examining  this  table  a  marked  similarity  is  to  be 
noticed  in  the  different  series ;  the  2 :  1  and  1 :  1  types  are 
common  to  all ;  the  4  :  1,  3  :  1,  3  :  2,  and  1  :  2  types  are  found 
in  all  but  one ;  while  2  :  3  types  are  found  in  three  of  the 
series.  Besides  the  seven  types  just  mentioned  there  are  eight 
others,  but  only  one  of  the  latter  exists  in  more  than  one 
series,  and  most  of  them  are  represented  by  only  a  single  salt. 
It  is  quite  possible  that  some  of  these  unusual  ratios  are  due 
to  erroneous  descriptions  of  salts,  but  it  is  certain  that  many 
of  them  represent  real  compounds. 

The  remarkable  similarity  in  the  prominent  types  of  the 
series  of  different  valencies  leads  to  the  conclusion  that  the 
valency  of  a  negative  Tialide  has  no  influence  upon  the  types  of 
double  salts  that  it  forms.  For,  if  valency  had  an  influence,  it 
would  be  expected  that  the  five  series  would  show  marked 
differences  from  one  another,  and  probably  the  halides  of 
higher  valency  would  tend  to  combine  with  a  larger  number 
of  alkaline  halide  molecules.  Instead  of  progression  of  types 
as  valency  increases,  however,  the  tables  show  a  marked 
symmetry  in  types,  and  their  arithmetical  limits  in  both  direc- 
tions are  as  nearly  constant  as  could  be  expected  considering 
the  variations  in  the  numbers  of  known  salts  in  the  different 
series.  The  prominence  of  the  3 :  1  and  3 :  2  types  in  the 
trivalent  series  may  perhaps  be  taken  as  an  indication  that  the 
rule  is  not  absolute,  but  since  these  types  are  not  the  only 
prominent  ones,  and  since  both  of  them  occur  in  three  other 
series,  the  circumstance  that  many  are  found  in  the  trivalent 
series  may  be  accidental. 

The  facts,  mentioned  above,  that  the  ratios  of  the  different 
series  are  nearly  symmetrical  and  that  the  arithmetical  limits 
of  the  types  in  loth  directions  are  nearly  uniform  appear  to  be 
important,  for  they  indicate  that  the  ratios  according  to  which 
positive  and  negative  halides  combine  are  not  influenced  to 
any  great  degree  by  the  positive  or  negative  nature  of  the 
halides.  In  other  words,  the  molecules  of  alkaline  halides 
possess  nearly  the  same  combining  power  as  molecules  of  negative 
halides.  Perhaps  this  point  may  be  made  clearer  by  the  state- 

28 


434  GENERALIZATIONS  ON 

ment  that  if  all  the  ratios  in  the  table  are  read  backward  they 
remain  almost  unchanged  in  their  arithmetical  aspect,  and  in 
the  cases  of  most  of  the  prominent  ratios  there  is  actually  no 
change ;  for  instance,  the  list  of  ratios  5  :  1,  3  :  1,  2  :  1,  3  :  2, 
1  :  1,  2  :  3,  1  :  2,  1  :  3  and  1  :  5  is  the  same  whether  read  for- 
ward or  backward,  and  to  these  ratios  belong  almost  95  per 
cent  of  the  salts  here  considered.  It  is  evident,  however,  that 
positive  and  negative  halides  are  not  of  exactly  equal  numerical 
importance,  for  to  the  left  of  the  1  :  1  ratio  in  the  table,  toward 
the  positive  halide  end,  the  ratios  are  more  numerous  and  the 
salts  far  more  abundant  than  toward  the  negative  halide  end ; 
it  appears  to  be  the  3  :  2  ratio  column  that  forms  a  nearly 
symmetrical  dividing  line  between  the  positive  and  negative 
ends,  and  even  with  this  division  the  salts  on  the  positive  side 
predominate  in  number. 

Another  point  to  which  attention  may  be  called  is  that  salts 
of  simple  types  predominate.  More  than  71  per  cent  of  the 
salts  in  the  list  belong  to  the  2 :  1  and  1 : 1  ratios,  while  the 
4  :  1,  3  :  1,  3  :  2,  2  :  3,  and  1 :  2  ratios  represent  over  25  per 
cent  of  them.  The  remaining  eight  types,  most  of  which  are 
more  complex,  include  less  than  three  per  cent  of  all  the 
salts.  The  fact  that  the  2  :  1  and  1  :  1  ratios  are  so  important 
in  all  the  series  is  another  indication  that  valency  does  not 
influence  the  ratios  according  to  which  halides  combine. 
Another  evidence  of  simplicity  is  the  circumstance  that  as  far 
as  is  known  not  more  than  five  molecules  of  one  halide  can 
combine  with  one  molecule  of  another  in  extreme  cases,  while 
the  usual  limit  is  2,  3,  or  4.  It  is  undoubtedly  a  fact  that 
there  are  a  few  complicated  salts  which  are  not  derived  from 
mixtures  or  poor  analyses.  For  example,  the  antimony  salts 
to  which  is  here  given  the  7 :  3  ratio  have  been  thoroughly 
investigated,  and  without  doubt  possess  either  this  ratio  or  one 
still  more  complex. 

The  conclusions  that  have  been  reached  above  are  not 
encouraging  in  the  way  of  giving  an  insight  to  the  structure 
of  double  halides,  for,  if  valency  plays  no  part  in  this,  the 
number  of  halogen  atoms  likewise  has  no  influence,  and  such 


DOUBLE  HALOGEN  SALTS.  435 

laws  or  rules,  based  on  halogen  atoms,  as  have  been  advanced 
must  be  abandoned.  Professor  Remsen's  law,*  which  states 
that  the  number  of  alkaline  halide  molecules  that  can  combine 
with  a  negative  halide  molecule  is  not  greater  than  the  valency 
of  the  latter,  is  one  of  these.  The  stepped  line  in  the  table  of 
ratios  shows  a  region  in  the  upper  left-hand  corner  which  is 
beyond  the  domain  of  this  law.  At  the  tune  that  the  law  was 
brought  forward  it  seemed  reasonable,  for  there  were  only  two 
or  three  possible  exceptions  to  it.  With  our  present  knowl- 
edge of  the  subject,  however,  it  is  evident  that  it  is  an  acci- 
dental circumstance  that  the  law  applies  to  so  many  double 
halides,  for  it  is  the  small  number  of  known  double  halides  of 
univalent  negative  metals,  as  well  as  the  rarity  of  salts  of  high 
alkali-metal  ratios  in  the  subsequent  series,  which  determines 
the  comparatively  small  number  of  exceptions  to  this  rule. 
Werner's  theory,!  depending  as  it  does  upon  definite  numbers 
of  halogen  and  other  atoms,  appears  to  have  no  application  to 
the  double  halides  in  general.  Possibly  it  may  apply  to  the 
salts  that  form  complex  ions  in  solution. 

A  prevalent  idea  concerning  the  influence  of  valency  in  the 
formation  of  simple  oxygen  salts  seems  to  need  revision  also, 
for  halogen  and  oxygen  salts  appear  to  be  governed  by  the 
same  laws.  For  instance,  there  is  no  good  reason  for  consid- 
ering the  valency  of  sulphur  to  have  an  influence  upon  the 
types  of  sulphates  that  can  exist,  and  consequently  for  imagin- 
ing an  ideal  or  "  ortho  "  sulphate  such  as  K6SO6. 

As  far  as  double  oxygen  salts  are  concerned,  there  can  be 
little  doubt  that  they  are  analogous  to  double  halogen  salts. 
Their  molecules  usually  unite  in  2  :  1  or  1  :  1  ratios.  A 
double  oxygen  salt,  however,  in  view  of  the  analogy  between 
double  halogen  and  simple  oxygen  salts,  may  be  considered  as 
analogous  to  a  double-double  halogen  salt,  if  such  there  be. 
Possibly  some  of  the  complex  types  of  double  halogen  salts 
may  be  due  to  such  combinations;  for  instance,  2RbaSbCl6 
(unknown)  +  RbSbCl4  =  7RbC1.3SbCl3. 

*  Amer.  Chem.  Jour.,  xi,  296 ;  xiv,  85. 
t  Zeitschr.  anorg.  Chem.,  iii,  267. 


436  GENERALIZATIONS  ON 

The  stability  of  double  halogen  salts  when  they  are  dissolved 
in  water  varies  exceedingly,  but  since  gradations  occur,  and 
there  is  no  sharp  dividing  line  between  classes  of  different 
stability,  it  cannot  be  supposed  that  there  is  any  real  difference 
in  structure,  as  far  as  the  solid  state  is  concerned,  between 
these  different  classes.  In  fact,  salts  that  are  isomorphous  and 
evidently  strictly  analogous  vary  greatly  in  their  behavior  in 
solution ;  for  example,  the  octahedral  salts  K2PtCl6,  KaSnCle, 
and  KaPbCls.  Although  only  two  classes  of  double  salts,  based 
on  their  behavior  in  solution,  are  usually  recognized,  there  are 
three  more  or  less  distinctly  denned  groups.  The  first,  of 
which  K8PtCl6  is  an  example,  undergo  ionization  into  alkali- 
metal  ions  and  complex  negative  ions  with  little  or  no  de- 
composition into  the  simple  halides.  It  is  this  class  which 
displays  a  striking  similarity  to  simple  oxygen  salts.  They 
are  comparatively  few  in  number,  but  the  double  cyanides, 
which  are  probably  entirely  analogous  to  double  halides,  fur- 
nish many  examples  of  them.  The  second  group  consists  of 
salts  that  readily  separate  into  their  component  halides  in  solu- 
tion, but  which  may  be  recrystallized  unchanged  from  water  or 
from  dilute  acid  solutions.  To  the  third  class  belong  salts 
that  require  the  presence  of  an  excess  of  one  of  their  halides 
in  solution  in  order  that  they  may  be  formed.  Sometimes  the 
excess  required  is  very  great,  so  that  the  proportion  of  halides 
in  the  solution  is  widely  different  from  that  in  the  salt  that 
crystallizes  out.  It  is  by  varying  the  proportions  of  two 
halides  greatly  that  a  series  of  several  double  salts  may  some- 
times be  produced  from  them. 

The  fact  that  the  same  two  halides  may  unite  in  several 
proportions  to  form  different  double  salts  is  a  point  that  has 
been  sometimes  disregarded  by  chemists.  Some  investigators 
have  been  content  with  the  preparation  of  a  single  compound 
in  cases  where  several  might  have  been  produced.  This  is  a 
matter  that  should  be  borne  in  mind  in  the  study  of  the  physi- 
cal properties  of  solutions.  The  largest  number  of  double 
halides  that  have  been  produced  by  combining  two  simple 
halides  appears  to  be  five ;  for  instance,  five  csesium  mercuric 


DOUBLE  HALOGEN  SALTS.  437 

chlorides  and  five  caesium  antimonious  fluorides,  are  the  most 
extensive  series  of  this  kind  that  are  known.  Such  series 
appear  to  be  limited  by  a  sort  of  overlapping  of  conditions ; 
for  compounds  that  are  expected  from  analogy,  intermediate 
between  two  that  are  produced,  often  cannot  be  prepared,  and 
where  a  single  double  salt  is  very  stable  it  may  be  the  only 
one  that  can  be  made.  Where  several  double  halides  of  the 
same  two  simple  halides  exist,  it  is  usually  the  case  that  one  of 
them  is  the  most  stable  one,  and  that  this  is  produced  by  the 
recrystallization  of  the  others,  but  cases  occur  where  two  of 
the  salts,  at  least,  are  unchanged  by  recrystallizing. 

The  water  of  crystallization  of  double  halides  appears  to 
present  precisely  the  same  problem  as  in  the  case  of  simple 
salts,  for  we  find  double  salts  of  the  same  type  possessing  no 
water  and  varying  quantities  of  it,  and  no  good  evidence  is  to 
be  found  that  in  these  compounds  a  molecule  of  water  is 
equivalent  to  an  alkaline  halide  molecule,  a  relation  similar  to 
that,  for  example,  that  has  been  supposed  to  exist  between  the 
compounds  FeSO4.7H2O  and  FeSO4.(NH4)2SO4.6H2O. 

It  has  been  pointed  out  previously  *  that  double  halides 
seem  to  show  an  increase  in  stability  and  variety  from  the 
iodides  to  the  chlorides,  and  apparently  also  to  the  fluorides. 
It  is  probable  that  this  is  a  general  rule  among  these  compounds. 

It  has  been  shown  f  also  that  with  the  metals  magnesium, 
zinc,  cadmium,  and  mercury  the  tendency  to  form  double 
halides  increases  with  the  atomic  weights.  This  tendency  is 
found  in  other  cases  also,  but  from  a  comparison  of  the  zir- 
conium and  thorium  salts,  as  well  as  the  antimonious  and 
bismuth  salts,  it  seems  doubtful  that  this  is  a  rule  that  applies 
in  all  cases. 

It  has  been  found  in  some  cases  J  that  caesium  appears  to 
form  more  extensive  series  of  double  salts  than  the  other 
alkali-metals,  but  evidently  there  are  exceptions  to  this  rule, 
for  Wells  and  Campbell  §  were  unable  to  prepare  any  caesium 
magnesium  iodide,  although  both  ammonium  and  potassium 
magnesium  iodides  are  known. 

*  Amer.  Jour.  Sci.,  Ill,  xlvi,  431.  t  Ibid.,  xlvi,  434. 

}  Ibid.,  Ill,  xlvi,  223.  §  Ibid.,  432. 


438  GENERALIZATIONS   ON 

The  rule  advanced  by  Godeffroy  *  that  all  the  double  salts 
of  caesium  are  less  soluble  than  those  of  the  other  alkali 
metals,  while  true  in  most  instances,  is  apparently  not  invariable, 
for  Wells  and  Campbell  f  found  that  the  1  :  1  caesium-zinc 
salts,  if  they  exist  at  all,  are  too  soluble  to  be  crystallized  in  a 
satisfactory  condition,  although  corresponding  ammonium  and 
potassium  salts  are  known. 

Professor  Remsen  J  has  called  attention  to  the  fact  that  cer- 
tain double  halides  show  gradations  in  water  of  crystallization, 
increasing  with  the  atomic  weight  of  the  halogen  and  decreas- 
ing with  the  atomic  weight  of  the  alkali  metal.  An  inspection 
of  the  lists  of  salts  shows  that  there  are  many  instances  of 
analogous  salts  to  which  these  rules  apply,  particularly  in  the 
larger  amounts  of  water  in  sodium  and  lithium  salts  and  in 
iodides,  and  the  smaller  amounts  of  water  in  caesium  salts 
and  in  fluorides;  but,  taking  the  list  as  a  whole,  these  gra- 
dations are  not  very  striking,  and  there  are  a  few  apparent 
exceptions  to  them. 

It  has  been  noticed  in  some  cases  that  caesium  halides  com- 
bine with  a  greater  number  of  negative  halide  molecules  than 
do  other  alkaline  halides,  while  at  the  other  end  of  a  series 
more  molecules  of  a  lighter  alkaline  halide  than  of  a  caesium 
halide  may  combine  with  a  negative  halide.  For  instance,  the 
caesium-zirconium  and  potassium-zirconium  fluorides  §  show 
this  relation  in  the  following  ratios  of  their  salts : 

CsF  :  ZrF4 2:1         1:1         2:3 

KF:ZrF4    ...     3:1         2:1         1:1 

This  is  evidently  not  a  general  rule,  however,  for  there  is  a 
1  :  5  ammonium-mercuric  chloride  corresponding  to  the  extreme 
type  of  caesium-mercuric  chlorides,  while  at  the  positive  end 
the  caesium-lead  and  caesium-mercuric  salts  extend  farther  than 
the  salts  of  other  alkali  metals. 

*  Berichte,  ix,  1365.  t  Amer.  Jour  Sci.,  Ill,  xlvi,  434. 

t  Amer.  Chem.  Jour.,  xiv,  88. 

§  Wells  and  Foote,  Amer.  Jour.  Sci.,  IV,  i,  18. 


DOUBLE  HALOGEN  SALTS.  439 

Many  irregularities  appear  in  the  list.  Sometimes  fluorides, 
chlorides,  bromides,  and  iodides  seem  to  be  analogous,  but  often 
they  are  not.  There  are  some  curious  relations  of  this  sort. 
For  instance,  all  the  double  fluorides  of  tellurium  are  1  :  1 
salts,  while  the  other  tellurium  salts  belong  to  the  2  :  1  type ; 
there  is  only  one  chloride  among  twelve  1  :  1  thallic  salts, 
while  all  the  2  :  1  salts  and  nearly  all  the  3  :  1  salts  are 
chlorides. 

Perhaps  the  most  marked  case  of  uniformity  in  double 
halides  is  the  invariability  of  the  2  :  1  type  in  the  salts  of  the 
quadrivalent  platinum  group  metals,  and  this  type  predom- 
inates to  a  remarkable  extent  among  the  salts  of  the  other 
quadrivalent  elements.  There  are  several  other  well-marked 
groups,  such  as  the  1  :  1  magnesium  salts  with  six  molecules 
of  water,  the  2  :  1  chromium  and  ferric  salts  with  one  water, 
and  the  3  :  2  anhydrous  arsenious,  antimonious,  and  bismuth 
salts. 

It  may  be  stated  that  in  our  study  of  double  halides  about 
one-third  of  the  compounds  given  in  the  list  have  been  pre- 
pared in  this  laboratory.  Some  indications  of  regularity  have 
been  observed  in  connection  with  these  researches,  but  it 
must  be  admitted  that  the  results  have  been  negative  as  far  as 
throwing  light  upon  the  structure  of  this  class  of  compounds 
is  concerned. 

Summary.  —  In  the  present  discussion,  by  the  method  of 
comparison,  the  most  important  conclusion  appears  to  be  that 
the  valency  of  negative  halides  has  little  or  no  influence  upon 
the  types  of  double  halides  that  they  form. 

It  has  been  shown  also  that  the  combining  power  of  negative 
halides,  whatever  their  valency  may  be,  is  nearly  the  same  as 
that  of  alkaline  halides. 

Attention  has  been  called  to  the  prominence  of  simple  types 
among  these  double  salts. 

It  has  been  pointed  out  that  double  halides  probably  increase 
in  ease  of  formation  and  variety  from  the  iodides  to  the  fluo- 
rides ;  but  that  other  gradations  and  analogies  which  exist  in 
some  cases  are  probably  not  general. 


440  DOUBLE  HALOGEN  SALTS. 

The  classification  of  double  halides  into  three  groups  based 
upon  their  behavior  in  solution  has  been  advocated:  (1) 
Salts  that  form  complex  ions.  (2)  Other  salts  that  can  be 
recrystallized  from  water  or  dilute  acids.  (3)  Salts  that 
require  the  presence  of  an  excess  of  one  of  their  components 
for  their  formation. 

SHEFFIELD  SCIENTIFIC  SCHOOL, 
May,  1901. 


INDEX 


INDEX 


ALUMS,  gradations  in  the  properties  of, 

170,  190. 

Alums,  solubilities  of,  170,  190. 
Ammonium-cuprous  halides,  385. 
Ammonium-ferric  halides,  357. 
Ammonium-lead  halides,  283,  313. 
Ammonium  nitrates,  acid,  146. 
Autimonic  double  halides,  413. 
Antimony,  a  salt  of  quadrivalent,  139. 
Antimony  double  halides,  139,  320,394, 

407,413. 
Arsenic  double  halides,  300. 

BISMUTH  double  halides,  397. 

CADMIUM  double  halides,  334. 
Caesium-antimonic  halides,  413. 
Caesium-antimonious  halides,  407. 
Caesium-antimony    chloride,    quadriva- 
lent, 139. 

Caesium-arsenious  halides,  300. 
Caesium-bismuth  halides,  397. 
Caesium-bismuth  nitrate,  153. 
Caesium-cadmium  halides,  334. 
Caesium-chromium  halides,  381 . 
Caesium-cobalt  halides,  366. 
Caesium-cupric  halides,  347,  352. 
Caesium-cuprous  halides,  354. 
Caesium-ferric  halides,  357. 
Caesium-ferric  nitrate,  152. 
Caesium-gold  halides,  211. 
Caesium  iodate-periodate,  155. 
Caesium  iodates,  58. 
Caesium-lead  halides,  250,  313. 
Caesium-magnesium  halides,  342. 
Caesium  material,  purification  of,  142. 
Caesium-mercuric  halides,  218. 
Caesium-nickel  halides,  366. 
Caesium  nitrates,  acid,  146. 


Caesium  pentahalides,  48. 
Caesium  periodate,  155. 
Caesium,  preparation  of  pure  salts  of,  71. 
Caesium,  quantitative  determination,  71. 
Caesium-silver  halides,  30,  207. 
Caesium-tellurium  fluoride,  418. 
Caesium-tellurium  halides,  268. 
Csesium-thallic  halides,  370. 
Caesium-thorium  chlorides,  415. 
Caesium  trihalides,  10. 
Caesium-uranyl  chloride,  384. 
Caesium-zinc  halides,  342. 
Caesium-zirconium  fluorides,  390. 
Chromium  double  halides,  381. 
Cobalt  double  halides,  366. 
Copper  double  halides,  347,  352,  354, 

385. 

Cupric  double  halides,  347,  352. 
Cuprous  double  halides,  354,  385. 

FERRIC  double  halides,  357. 
Ferrous-ferric  bromides,  364. 

GENERALIZATIONS  on  double  halides, 

420. 
Gold  double  halides,  211. 

INORGANIC  compounds,  properties  of, 

158. 

Iodates,  alkali-metal,  58. 
Iron  double  halides,  357. 
Iron,  volumetric  determination  of,  97. 

LEAD  compounds  with  extra  iodine,  77, 

89. 
Lead  double  halides,  250,  283,  295,  313, 

77. 

Lead  tetrachloride  double  salts,  313. 
Lithium  peutahalide,  48. 


444 


INDEX 


Lithium-thallic  halides,  370. 
Lithium-zirconium  fluorides,  400. 

MAGNESIUM  double  halides,  342. 
Mercuric  double  halides,  218. 

NICKEL  double  halides,  366. 
Nitrates,  acid,  146. 
Nitrates,  double,  151. 

PECULIAR    halides   of    potassium  and 

lead,  77. 

Pentahalides,  alkali-metal,  48. 
Periodic  system,  158. 
Potassium-arsenious  halides,  300. 
Potassium-ferric  halides,  357. 
Potassium  ferricyanide,  an  isomer  of, 

116,  130. 

Potassium  ferrous-ferric  bromide,  369. 
Potassium  iodate-chloride,  68. 
Potassium-lead  halides,  250,  313,  77. 
Potassium-lead  halides,  peculiar,  77. 
Potassium  nitrate,  acid,  146. 
Potassium  pentahalide,  48. 
Potassium-silver  halides,  207. 
Potassium-tellurium  halides,  268. 
Potassium  trihalides,  33. 

RuBiDiUM-antimonious    halides,    320, 

394. 

Rubidium-antimony  oxychloride,  397. 
Rubidium-arsenious  halides,  300. 
Rubidium-ferric  halides,  357. 
Rubidium  ferrous-ferric  bromide,  364. 


Rubidium-gold  halides,  211. 
Rubidium  iodates,  58. 
Rubidium-lead  halides,  295,  313. 
Rubidium  nitrates,  acid,  146. 
Rubidium  pentahalide,  48. 
Rubidium-silver  halides,  207. 
Rubidium-tellurium  halides,  268. 
Rubidium-thallic  halides,  370. 
Rubidium  trihalides,  33. 

SILICIC  acid,  separation  from  tungstic 

acid,  136. 

Silver  double  halides,  207. 
Sodium  pentahalide,  48. 
Sodium-thallic  halides,  370. 
Sodium-zirconium  fluorides,  400. 

TELLURIUM  double  halides,  268,  418. 
Thallic  double  halides,  370. 
Thallium  triiodide,  84. 
Thallium-zirconium  fluorides,  400. 
Thallous  nitrates,  acid,  146. 
Thallous-thallic  nitrate,  154. 
Thorium  double  chlorides,  415. 
Titanic  acid,  volumetric  determination 

of,  97. 

Trihalides,  alkali-metal,  10,  33. 
Tungstic  acid,  separation  from  silicic 

acid,  136. 

VANADIUM,    compounds    of    trivalent, 
103. 

ZINC  double  halides,  342. 
Zirconium  double  fluorides,  390, 400. 


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